This morning, Israel launched a major military operation against Iran targeting its nuclear programme, including facilities, individual scientists and military leadership. In this post, I will provide a quick, preliminary analysis of the legality of Israel’s use of force against Iran as a matter of the jus ad bellum. As I will explain, Israel’s use of force against Iran is, on the facts as we know them, almost certainly illegal.
The only justification that Israel can provide for its use of force is self-defence under Article 51 of the Charter – using force to repel an armed attack, subject to the criteria of necessity and proportionality. The first point to clarify here is that the nature and stated goals of Israel’s use of force – damaging Iran’s nuclear programme and preventing it from developing a nuclear weapon that could be used against Israel – are explicitly about deflecting a future armed attack by Iran against Israel, i.e. an attack that is yet to occur. In other words, this is not a situation in which Israel is allegedly responding to an Iranian attack occurring now, whether directly or through proxies such as the Houthis. Prior uses of force between these two states can be legally and factually relevant as context, but the issue here is again squarely about stopping a future nuclear attack by Iran. Assessing the legality Israel’s use of force against Iran thus depends on the legal conception of self-defense being applied and on the facts to which the legal rules can be applied.
There are three possible legal positions (with some variations on a spectrum) on uses of force in response to future armed attacks:
- That states can act preventively to deflect threats, especially existential threats.
- That states can act to deflect future armed attacks that are imminent.
- That states can only act to deflect armed attacks that have occurred.
If one regards the third position as correct, then Israel’s use of force against Iran would be manifestly illegal. But, while it is difficult to reliably establish what the majority view on some of these issues is, I think we can say that reasonable scholars and states have argued that the third position is too restrictive.
We can easily say, however, that there is unanimous agreement among international lawyers that the first position is legally untenable. It is associated, for example, with some of the arguments that the lawyers in the Bush administration justified to use force against Iraq – that it might give weapons of mass destruction to terrorist actors who might use them against the United States and that the threat is so grave that the US would be defending itself from Iraq. It is also similar to arguments that Russia has used to justify its invasion of Ukraine – that Ukraine might attack Russia at some future point. The facts of these two examples aside, the problem with this approach is that it is so boundless that it completely eviscerates the prohibition on the use of force – a state could act whenever it perceives an existential threat. After all, Russia, the US and China have the ability to destroy each other within hours, but that kind of capability cannot automatically mean that they can start a war and call it self-defence.
In short, this ‘preventive’ form of self-defence is simply not self-defence at all. With regard to Iraq, even the UK, America’s closest ally, expressly disavowed such a legal theory (see here para 3), and even the US itself did not formally rely on this argument internationally.
Therefore, Israel could only justify its use for against Iran by relying on the second, intermediate position – that Iran’s nuclear attack on Israel was imminent. The question of anticipatory self-defence against imminent attacks has been much debated – for some background, see here. Broadly speaking, there are two theories of what an ‘imminent’ attack is. The first, restrictive one, is temporal in character – an imminent attack is one that is about to happen. The second, more expansive one, is causal in character – an imminent attack is one where the state concerned will obtain the capability to conduct the attack and intends (has irrevocably committed itself) to the attack at some point in the future. This more expansive approach is often coupled with the necessity of an immediate response today, e.g. that now is the ‘last possible window of opportunity’ to act to stop the imminent attack. (See also here, at 104-108).
On the temporal understanding of an imminent attack, there is simply no plausible way of arguing that Iran was about to attack Israel with a nuclear weapon, which it doesn’t even have. Thus, the only plausible legal theory of self-defence that Israel could invoke would be the causal, non-temporal one. Let’s assume, for the sake of the argument, that this theory is correct. If so, Israel could justify its use of force only if the following two propositions of fact were both true:
- That Iran’s leadership has irrevocably committed itself to attacking Israel with a nuclear weapon, once such a weapon has been developed, i.e. that it intends to attack Israel in the future once it has the capability to do so.
- That today was the last window of opportunity to stop the attack from happening, i.e. that it was necessary to act now and that no non-forcible alternative could have removed either Iran’s future capability or its intention to attack Israel.
Now, obviously, I am not privy to the information that say Israeli, American or British intelligence services have about the intentions of Iran’s leadership. Working solely from information that is publicly available, I would say that the situation as it stands is as follows:
- There are many public statements by various Iranian officials over the years calling, expressly or impliedly, for Israel’s destruction.
- That kind of rhetoric, however, is mainly meant for domestic political purposes in Iran and does not, without more, directly translate to an intention of the Iranian leadership to use a nuclear weapon against Israel, despite the fact that Israel itself already has nuclear weapons and could retaliate against Iran decisively.
- Maybe Israeli officials do have some intelligence about the intentions of Iran’s leaders – especially Ayatollah Khamenei – to attack Israel with nuclear weapons, but they have not provided any such intelligence publicly.
- This means that the first prong of the test above fails – there is little evidence, as things stand, that Iran intends to use a nuclear weapon against Israel once it obtains the capability to do so. Inflammatory, even genocidal, public statements by some Iranian officials do not suffice on their own, because they are not sufficiently probative about the intent of those Iranian officials who actually make the relevant decisions.
- Even according to the Israeli prime minister, Iran was months from building a bomb, while negotiations between the US and Iran were actively taking place. (Note how the UNSG expressed his concern about ‘Israeli attacks on nuclear installations in Iran while talks between Iran and the United States on the status of Iran’s nuclear programme are underway.’)
- Thus, while militarily Israel undoubtedly found itself in a convenient position to attack Iran, which was already weakened due to prior engagements between the two states, it is difficult to see how today was the ‘last window of opportunity’ to deflect a future nuclear attack, i.e. that the use of force was necessary, the only available option to stop this attack.
To conclude, even if the broadest possible (legally plausible) understanding of anticipatory self-defence was taken as a correct, Israel’s use of force against Iran would be illegal. This is because there is little evidence that Iran has irrevocably committed itself to attacking Israel with a nuclear weapon, once it develops this capability. And even if such an intention was assumed – again, it would be for Israel to provide any further evidence of such intention – I don’t see how it could plausibly be argued that using force today was the only option available.
This post was limited to an ad bellum analysis – in short, unless Israel is able to provide substantially more compelling evidence than is currently publicly available, it cannot reasonably be argued that Iran would imminently attack Israel, or that using force was the only option to stop that attack. Israel is therefore using force against Iran unlawfully, in violation of Article 2(4) of the Charter. It is committing aggression.
There are also in bello issues to be discussed. One point that I found particularly problematic is the apparent direction of attacks specifically against Iranian scientists working for the nuclear programme. If such scientists are members of Iran’s armed forces, they are combatants and can lawfully be targeted as a matter of IHL. But scientists who are civilians – and most probably are – cannot (as persons) lawfully be made the object of an attack. Simply working on a weapons programme as a researcher does not entail direct participation in hostilities that could remove civilian immunity from an attack. To give an analogy, the hundreds of civilian scientists or engineers who worked on the Manhattan Project would not (in today’s terms) be qualified as combatants or civilians taking a direct part in hostilities. The facilities in which they worked would qualify as military objectives (as would a munitions factory, for instance). But the scientists themselves as persons would not.
Is Israel’s Use of Force Against Iran Justified by Self-Defence?
Written by Marko MilanovicThis morning, Israel launched a major military operation against Iran targeting its nuclear programme, including facilities, individual scientists and military leadership. In this post, I will provide a quick, preliminary analysis of the legality of Israel’s use of force against Iran as a matter of the jus ad bellum. As I will explain, Israel’s use of force against Iran is, on the facts as we know them, almost certainly illegal.
The only justification that Israel can provide for its use of force is self-defence under Article 51 of the Charter – using force to repel an armed attack, subject to the criteria of necessity and proportionality. The first point to clarify here is that the nature and stated goals of Israel’s use of force – damaging Iran’s nuclear programme and preventing it from developing a nuclear weapon that could be used against Israel – are explicitly about deflecting a future armed attack by Iran against Israel, i.e. an attack that is yet to occur. In other words, this is not a situation in which Israel is allegedly responding to an Iranian attack occurring now, whether directly or through proxies such as the Houthis. Prior uses of force between these two states can be legally and factually relevant as context, but the issue here is again squarely about stopping a future nuclear attack by Iran. Assessing the legality Israel’s use of force against Iran thus depends on the legal conception of self-defense being applied and on the facts to which the legal rules can be applied.
There are three possible legal positions (with some variations on a spectrum) on uses of force in response to future armed attacks:
If one regards the third position as correct, then Israel’s use of force against Iran would be manifestly illegal. But, while it is difficult to reliably establish what the majority view on some of these issues is, I think we can say that reasonable scholars and states have argued that the third position is too restrictive.
We can easily say, however, that there is unanimous agreement among international lawyers that the first position is legally untenable. It is associated, for example, with some of the arguments that the lawyers in the Bush administration justified to use force against Iraq – that it might give weapons of mass destruction to terrorist actors who might use them against the United States and that the threat is so grave that the US would be defending itself from Iraq. It is also similar to arguments that Russia has used to justify its invasion of Ukraine – that Ukraine might attack Russia at some future point. The facts of these two examples aside, the problem with this approach is that it is so boundless that it completely eviscerates the prohibition on the use of force – a state could act whenever it perceives an existential threat. After all, Russia, the US and China have the ability to destroy each other within hours, but that kind of capability cannot automatically mean that they can start a war and call it self-defence.
In short, this ‘preventive’ form of self-defence is simply not self-defence at all. With regard to Iraq, even the UK, America’s closest ally, expressly disavowed such a legal theory (see here para 3), and even the US itself did not formally rely on this argument internationally.
Therefore, Israel could only justify its use for against Iran by relying on the second, intermediate position – that Iran’s nuclear attack on Israel was imminent. The question of anticipatory self-defence against imminent attacks has been much debated – for some background, see here. Broadly speaking, there are two theories of what an ‘imminent’ attack is. The first, restrictive one, is temporal in character – an imminent attack is one that is about to happen. The second, more expansive one, is causal in character – an imminent attack is one where the state concerned will obtain the capability to conduct the attack and intends (has irrevocably committed itself) to the attack at some point in the future. This more expansive approach is often coupled with the necessity of an immediate response today, e.g. that now is the ‘last possible window of opportunity’ to act to stop the imminent attack. (See also here, at 104-108).
On the temporal understanding of an imminent attack, there is simply no plausible way of arguing that Iran was about to attack Israel with a nuclear weapon, which it doesn’t even have. Thus, the only plausible legal theory of self-defence that Israel could invoke would be the causal, non-temporal one. Let’s assume, for the sake of the argument, that this theory is correct. If so, Israel could justify its use of force only if the following two propositions of fact were both true:
Now, obviously, I am not privy to the information that say Israeli, American or British intelligence services have about the intentions of Iran’s leadership. Working solely from information that is publicly available, I would say that the situation as it stands is as follows:
To conclude, even if the broadest possible (legally plausible) understanding of anticipatory self-defence was taken as a correct, Israel’s use of force against Iran would be illegal. This is because there is little evidence that Iran has irrevocably committed itself to attacking Israel with a nuclear weapon, once it develops this capability. And even if such an intention was assumed – again, it would be for Israel to provide any further evidence of such intention – I don’t see how it could plausibly be argued that using force today was the only option available.
This post was limited to an ad bellum analysis – in short, unless Israel is able to provide substantially more compelling evidence than is currently publicly available, it cannot reasonably be argued that Iran would imminently attack Israel, or that using force was the only option to stop that attack. Israel is therefore using force against Iran unlawfully, in violation of Article 2(4) of the Charter. It is committing aggression.
There are also in bello issues to be discussed. One point that I found particularly problematic is the apparent direction of attacks specifically against Iranian scientists working for the nuclear programme. If such scientists are members of Iran’s armed forces, they are combatants and can lawfully be targeted as a matter of IHL. But scientists who are civilians – and most probably are – cannot (as persons) lawfully be made the object of an attack. Simply working on a weapons programme as a researcher does not entail direct participation in hostilities that could remove civilian immunity from an attack. To give an analogy, the hundreds of civilian scientists or engineers who worked on the Manhattan Project would not (in today’s terms) be qualified as combatants or civilians taking a direct part in hostilities. The facilities in which they worked would qualify as military objectives (as would a munitions factory, for instance). But the scientists themselves as persons would not.
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Alex Fox says
June 13, 2025
In my view, it is deeply problematic that, following the Israeli attacks—which, incidentally, killed several civilian women and children in residential areas of Iran, a fact that this post does not even mention—the focus is on whether the attacks were legally justified. The post gives the impression that the strikes “targeted [Iran’s] nuclear programme,” while ignoring the very real and tragic human cost.
Framing the question in such a way—even if the author ultimately concludes that the attacks were unlawful—reinforces a troubling narrative. It presents what is a straightforward issue as if it were legally complex or open to interpretation. To illustrate the problem: imagine a post that explores whether the actions of Nazi Germany were legally justified. Even if the author spends pages outlining the reasons why they were not, the mere act of entertaining the question in this way risks lending unwarranted legitimacy to the idea that there was something worth debating.
Equally concerning is the author’s apparent effort to craft the post in a manner that diplomatically avoids offending “some people.” For example, when the post states, “Maybe Israeli officials do have some intelligence”, or refers to a lack of proof by saying “there is little evidence, as things stand,” it raises the question of whether the same cautious and equivocal phrasing would be used in other contexts. Would the same author say, “Maybe Russian officials do have some intelligence” or “there is little evidence, as things stand,” that Ukraine is committing genocide?
I sincerely hope we will see an end to such double standards in international legal scholarship. More importantly, I hope that EJIL:Talk and our esteemed colleague Marko will allow this comment to be published in the spirit of open, honest, and critical debate.
Eitan Diamond says
June 13, 2025
Thanks Marko for this incredibly quick and sharp analysis. I fully agree with your compelling argument that (barring unknown facts) if Israel’s use of force last night was undertaken only with the view to deflect future armed attacks by Iran, then it was almost certainly illegal. I anticipate however, that the first point you make – namely that the nature and stated goals of this use of force were such that it should be examined in distinction from previous clashes between Israel and Iran – will be challenged by some. Would be interested to hear more about how you would respond to the likely argument that the attacks last night were part of an ongoing international armed conflict and that Israel’s action was influenced not only by projections into the future but also by Iranian attacks that have already occurred during earlier stages of the hostilities.
Marko Milanovic says
June 13, 2025
Dear Alex,
Thank you for your comment. I really don't see what the double standards are. Arguments about self-defence (and the jus ad bellum) are necessarily factually contingent. Some facts ARE uncertain - at least on the evidence publicly available. The Russia/Ukraine example is different simply because there is literally no evidence that Ukraine would ever attack Russia, whereas there is plenty of evidence that Iran and Israel would attack each other, and have done so in the past. Frankly I also think a Nazi comparison is completely inappropriate - if for no reason that there is again literally zero evidence that Poland would have attacked the Third Reich. Iran IS developing a nuclear weapon, or a programme that can easily lead to weapon. It is not simply one designed for peaceful purposes, if nothing else because the level of enrichment of uranium in their stockpiles far exceeds anything needed for peaceful purposes. So saying that Israel is Nazi Germany while Iran is Poland, and that Israel has no good reason to be concerned about Iran's nuclear programme, is at best unhelpful.
I did not talk about civilian loss of life (with the exception of the scientists) simply because the facts of that are still evolving and because my post was focused on the jus ad bellum. The mere fact that civilians were killed does not entail that attacks were directed at them (they could have been harmed incidentally, which is not necessarily unlawful). On the other hand, the scientists were killed deliberately, and if they were civilians - and at least some were - that is a violation of the principle of distinction and potentially a war crime.
Marko Milanovic says
June 13, 2025
Dear Eitan,
Many thanks for that comment. I agree with you that the kind of argument you outline would be used in Israel's favour. But I don't think it makes much sense, legally or factually. The there may already exist an international armed conflict is an in bello matter which cannot affect an ad bellum analysis. That there have been prior attacks by Iran against Israel - most of which are actually over, and to the extent they are continuing are of minimal intensity - cannot justify (in terms of necessity and proportionality) an all out assault on Iran's nuclear programme. In other words, I fail to see how it could be said that some ongoing Iranian attack is being stopped by say striking Natanz - all it does in today's terms is to increase the possibility that Iran will launch conventional attacks against Israel.
So, in brief, the only argument that can possibly work is the necessity to stop a future attack. Iran's prior conduct is evidence of Iran's intent, and to that extent it is certainly relevant. Thus, Iran's past behaviour and adversarial relationship to Israel certainly makes it more plausible to argue that, if it had a nuclear weapon, Iran would use it against Israel. But all that does is raise the threat level, as it were. There is still not enough evidence, at least that I can see, that Iran is building a nuclear weapon to use it against Israel, i.e. that it has committed itself irrevocably to such an attack.
Yotam Dov says
June 13, 2025
Iran has explicitly said that it wants Israel wiped off the map - literally. For Israel, there is no other option.
Remember, before the Islamist, fundamentalist revolution that buried all Western values and aimed to drag the country back to the medieval age, Iran was a decent, flourishing state. Many Israeli businesses operated there, with direct flights between Tehran and Tel Aviv.
Why would a country, 2,000 kilometers away from Israel, with no direct conflict, suddenly decide it wants to wipe another country off the map? What would you do?
It feels like the discussion is always centered around Israel - perhaps because it upholds certain values. Yet no one seems to raise questions about Iran being an extreme, oppressive regime that supports terror through proxies: the Houthis in Yemen, Hezbollah, Assad massacring his own people in Syria, and involvement in Sudan.
Alex Fox says
June 13, 2025
Dear Marko,
I believe you are far too perceptive to overlook the real issue at stake here.
As you know, negotiations have been ongoing—hopefully still are—between Iran and the US regarding Iran’s nuclear program. Initially, the US expressed concern about the potential weaponization of Iran’s nuclear activities, to which Iran immediately responded with willingness to address. However, the US later shifted its position, insisting that there should be no uranium enrichment on Iranian soil at all—a demand that Iran cannot reasonably accept, particularly given its rights under international law to pursue peaceful nuclear enrichment.
Until very recently—indeed, until this week—a new round of negotiations was expected, with hope for progress toward a compromise. There is no active armed conflict between Iran and Israel, nor is there credible evidence that Iran intends to develop or deploy nuclear weapons against Israel.
Also, Israel had not taken any overt military action against Iran for months. Then, suddenly, just days before this critical round of negotiations, Israel launched an attack inside Iran, killing not only civilians, public officials, and nuclear scientists, but also, notably, targeting a senior Iranian official who was directly involved in the negotiation process—though it remains unclear whether he survived the attack. I find it difficult to believe this is merely coincidental or tied to Israel’s "longstanding justifications". Rather, the timing strongly suggests a deliberate attempt to sabotage the diplomatic process between Iran and the US.
If one truly has concerns about Iran's nuclear program, wouldn’t supporting diplomatic efforts and potential agreements be the logical course of action? I genuinely wonder why!
Olivia Flasch says
June 13, 2025
I think this post disregards the argument that Israel and Iran have been directly engaged in an international armed conflict with one another at the very least since Iran's ballistic missile attack on Israel in April of last year (though it may be argued, even earlier than that through Iran's substantial involvement to non-state armed groups in the area). If that is the case, then a self-defence argument at this stage is irrelevant and unnecessary. I am wondering if this is something the author has considered - and if you have reason to believe the parties are not currently engaged in an international armed conflict?
See e.g.https://lieber.westpoint.edu/iran-party-international-armed-conflict-israel/
Marko Milanovic says
June 13, 2025
Dear Olivia,
I am happy to concede that at various points in the recent past there was an IAC between Iran and Israel. I'm happy to concede even that there was one yesterday. But that is squarely a matter of IHL. It, in my view, has no relevance to the application of the prohibition on the use of force in Art 2(4) of the Charter. Either state still needs an ad bellum justification to use force. The existence of an IAC is not such a justification. There is also ample authority (including some in the recent ICJ AO on the occupied territories) that an ad bellum assessment is a continuing one, not simply one done at the start of a conflict.
Ori Pomson says
June 13, 2025
Thank you Marko for this post. Just two quick observations. First, on the ad bellum issue, I wonder whether the analysis views the present attacks too much in isolation from what is legally an ongoing and wide-reaching conflict between the states, particularly (but not only) in light of Iran's so-called "indirect" armed attacks against Israel through substantial involvement (within the meaning of UNGA Resolution 3314) in Hezbollah and Houthi attacks, not to mention Hamas. In other words, it is a stage of the conflict where proportionality plays a less restrictive role (in Greenwood's sense at 223 here: https://www.jstor.org/stable/pdf/20096988.pdf), so that going after the adversary's latest (but much more deadly than any other) weaponry capability is permitted.
Second, regarding in bello, I think the issue of targeting nuclear scientists, at least those who provide a unique and crucial contribution to a nuclear weapons program, is more nuanced. In this regard, even the ICRC’s DPH Interpretative Guidance – not known for its expansive understanding of DPH – entertains this possibility (at footnote 122: https://www.icrc.org/sites/default/files/external/doc/en/assets/files/other/icrc-002-0990.pdf).
Olivia Flasch says
June 13, 2025
Thank you for your response, Marko. I take it then that you disagree with this statement of Geoff Corn, in the following article: "But international law does not require a distinct self-defense justification for every use of force in the context of an ongoing armed conflict. This does not mean international law plays no role in such situations; quite the contrary. But once an armed conflict is ongoing, the legality of military response is established and international law shifts to regulating the manner of operational execution."
https://sites.duke.edu/lawfire/2023/03/28/guest-post-geoff-corn-on-the-united-states-and-iran-are-in-an-armed-conflict-and-it-is-time-to-act-accordingly/
Marty Lederman says
June 13, 2025
I agree with you, Marko, that if this were a true "first strike," it'd obviously breach Article 2(4) of the Charter. See my post here, including footnote 4 on the 1981 Orisak reactor strike:
https://www.justsecurity.org/30522/egan-speech-bush-doctrine-imminence-necessity-first-use-jus-ad-bellum/
I had the same reaction as Olivia, though: *If* Israel and Iran are already engaged in an IAC that involves cross-border strikes against one another (which I assume will be Israel's view--I'd be surprised if they submit an Article 51 letter), the Article 2(4) question is simply inapposite, no? It can't be that every cross-border attack in an ongoing IAC requires a separate Article 51 analysis. What am I missing?
On the targeting of scientists, is this the first time that any state has *acknowledged* doing so? If so, I think it's setting a very ominous and dangerous precedent. As you know, Hays Parks was committed to the idea that they're DPH. See n.294 here: https://ogc.osd.mil/Portals/99/Law%20of%20War%202023/DOD-LAW-OF-WAR-MANUAL-JUNE-2015-UPDATED-JULY%202023.pdf?ver=Qbxamfouw4znu1I7DVMcsw%3D%3D#page=266
Parks never established that that was the CIL view, however. And as Part 4-a of this report reflects, I'm not aware there's been an established consensus view:
https://www.icrc.org/sites/default/files/external/doc/en/assets/files/other/2006-03-report-dph-2006-icrc.pdf#page=46
Is there any worthwhile scholarship on the question?
Marko Milanovic says
June 13, 2025
Dear Ori and Olivia,
Many thanks for this. On the ad bellum point:
1) Re Geoff's statement, he is right in that, in many scenarios, once a war starts from an operational lawyer's point of view no further ad bellum analysis is necessary. If one is say a Ukrainian army lawyer, one doesn't have to do an ad bellum analysis when say selecting targets for attack in Russia. But that's simply because the ad bellum legality of this is obvious. It's also because the intensity of the ongoing armed attack by Russia on Ukraine is so overwhelming that basically any military response to it would be necessary and proportionate (assuming IHL compliance).
In such situations, a separate ad bellum analysis might be done for major escalatory steps (e.g. occupying parts of Russian territory, as in Kursk), or if the Russian attacks recede.
From a Russian perspective, no ad bellum analysis is necessary because ALL OF IT is ad bellum unlawful, every single bullet.
My point is simply that this is nowhere near like the situation in which there's the occasional Hezbollah or Houthi missile fired against Israel, on the assumption that these actors act on Iran's behalf. If THAT is the ongoing armed attack by Iran, I can't see how it could be necessary and proportionate to bomb Iranian nuclear facilities, kill the whole military leadership, attack god knows how many other targets etc.
The only plausible position here is that doing all of this is necessary to stop a future attack. (The prior history is probative of the intent to commit that future attack - that's why Israel is rightly concerned about an Iranian nuclear attack, and not about a Russian nuclear attack, even though Russia already has the nukes). And in fact - from what I gather - this is precisely what Israeli leaders have been saying, that the purpose of the use of force is to stop Iran for using nuclear weapons against Israel in the future. If that is how they describe their purpose, I fail to see why we should reorient ourselves to the supposed or real ongoing attack.
2) Ori as for the DPH point, I'm not sure the ICRC Guidance can be said to entertain the possibility. It is simply reporting the views of experts in the meetings the ICRC had convened. And it was in fact only one expert who entertained the possibility. The full quote from the 2006 DPH report, which is what that fn refers to, is below. Honestly I find it difficult to accept the proposition that Oppenheimer, Fermi and the hundreds of other civilian scientists who worked on the Manhattan Project were actually DPH-ing (in modern terms) and could have been lawfully killed by Nazi assassins as they slept in their beds. If you go so far, I fail to see how any civilian researcher, AI developer, engineer whose work can be put to military use would also then not be a lawful target. The 'nukes are extreme/special' point is not a terribly persuasive one, at least in my view.
Quote:
In response, several experts insisted that there has been a consensus since the Second World War that neither armament industry employees, nor nuclear weapons experts, were considered to be directly participating in hostilities regardless of their value to the war effort.
While they could not be individually directly attacked, they often assumed an increased risk of incidental death or injury because their working places constituted legitimate military
objectives. One of the experts also pointed out that, if working in a state’s armament industry or being a nuclear weapons expert were regarded as direct participation in hostilities, the
concerned persons would either have to be incorporated into the armed forces, or would have to be regarded as unprivileged combatants. Another expert additionally clarified that, even if working in an ammunition factory were to be regarded as direct participation in hostilities, the individual workers could only be directly attacked “for such time as” they were actually working in the factory, a time frame during which they would be exposed to attacks
against the factory itself anyway. One of the experts, while agreeing with the principle that a civilian weapons expert should not lose protection against direct attack, nevertheless
doubted whether this assessment could be maintained in extreme situations where the expertise of a particular civilian was of very exceptional and decisive value for the outcome of an armed conflict. For example, in the case of nuclear weapons experts during the Second World War, the enormous importance of the individual contribution to the war effort clearly
exceeded the ordinary and could perhaps have lead to a conclusion deviating from the general rule.
At 49 https://www.icrc.org/sites/default/files/external/doc/en/assets/files/other/2006-03-report-dph-2006-icrc.pdf
Marko Milanovic says
June 13, 2025
Marty, I saw your comment only after replying to Ori and Olivia, so I hope my points there answer your question re the ad bellum.
To simplify this, if there was an exchange of fire at the India/Pakistan border, with 10 people killed on each side, there would undoubtedly be an IAC. But - regardless of who started it! - that would not give either state the right to start an enormous bombing campaign to militarily defeat their adversary (for example). Why? because of the continuing operation of necessity and proportionality - that is the point of these criteria.
Re DPH, maybe Hays Parks was that one expert at the ICRC DPH meeting in 2006! I am not, off the top of my head, familiar with any academic articles specifically discussing whether scientists are DPH-ing (happy to read them!).
Mary Ellen O'Connell says
June 13, 2025
Dear Marko,
The alacrity of your analysis is admirable, as is your evident support for the importance of international law on the use of force. I am writing from the United States, however, where decades of creating exceptions and reinterpretations of law helps explain our leadership’s contempt for the law today.
The United Nations Charter has one standard for the use of force in self-defense, not three. The right arises “if an armed attack occurs”. The right does not depend on what is in the minds of national leaders or the lethality of weapons.
A state victim of aggression is also governed by the Charter and the principles of attribution, necessity and proportionality. Iran can halt and repel Israel’s attacks but is restricted from attacking Israel because doing so would be pointless, owing Israel’s effective defensive shields. Iran has squandered its resources by failing to build its own defensive shield.
The existence of nuclear weapons and the persistent use of military force to retaliate or to signal resolve relate to 1940s realist-deterrence theory. The theory is based on projecting military force regardless of the law. Militaries are programming AI-enhanced computers with deterrence-based data at this moment. They are not inputting the authentic law of self-defense. Geoffrey Hinton, the father of AI, sees us heading to human extinction.
But AI also has the antidote. A shift to defensive shield systems that are more effective than the violent mind games of deterrence, plus diplomacy, can lead to the end of nuclear weapons, proxy wars, and the rest. It can give us the courage to speak legal truth to power.
With best regards,
Mary Ellen
Ori Pomson says
June 13, 2025
Thank you Marko and Marty for engaging. Re DPH, to my understanding, Avril McDonald also took that position (here at page 18: https://www.asser.nl/upload/wihl-webroot/documents/cms_ihl_id70_1_McDonald%20DPH%20-%20April%202004.doc). It would also seem that Mike Schmitt's position (at least at the time, in "„Direct Participation in Hostilities“
and 21st Century Armed Conflict") would extend to such persons, so I would suspect that there were more experts involved in the DPH Guidance process (before it was terminated) who would have agreed. I would only just add on this point that the argument is much more modest than a contention that the hundreds of scientists who participated in the Manhattan Project would have been targetable. It would rather appear it would solely extend to persons whose contribution is a irreplaceable in developing a game-changing technology designed to be employed in a specific conflict.
Re Marty's question on scholarship, more recently Eran Shamir-Borer addressed it at relative length here (pages 967-71): https://cdn.vanderbilt.edu/vu-wp0/wp-content/uploads/sites/78/2018/06/07024021/18.-Shamir-Borer_Final-Review_Formatted.pdf
Shimon Cohen says
June 13, 2025
While the author provides a thoughtful analysis, it seems that the unique circumstances surrounding Iran's nuclear program require additional consideration. Specifically, the critical distinction here is that Iran was reportedly on the verge of developing a nuclear weapon—mere months away, according to available intelligence. In the days immediately preceding the Israeli operation, reports indicated further alarming developments: according to the IAEA Board of Governors' resolution on June 12, 2025, Iran was found to be in violation of its non-proliferation obligations, operating undisclosed enrichment facilities and stockpiling uranium beyond permitted levels. See https://www.reuters.com/world/china/iaea-board-declares-iran-breach-non-proliferation-duties-diplomats-say-2025-06-12. A detailed IAEA report from late May 2025 also confirmed secret nuclear-related activities and enriched uranium nearing weapons-grade levels. See https://www.reuters.com/world/china/iaea-report-says-iran-had-secret-activities-with-undeclared-nuclear-material-2025-05-31. Additionally, Israeli officials have warned that Iran could "break out" to a nuclear weapon within a few months.
Unlike general scenarios of anticipatory self-defence, a nuclear threat approaching this advanced stage arguably alters the traditional calculus. At such a juncture, waiting until the attack is truly "imminent" in a conventional temporal sense risks becoming effectively meaningless, as the window to effectively neutralize the threat would already have closed.
Admittedly, from a strictly doctrinal perspective of international law, as the author articulates, Israel's action may be deemed illegal. However, I believe this situation exposes a fundamental weakness in the international legal framework. The laws governing the use of force were designed primarily in a different era, for conflicts between conventional states—not for cases where an openly hostile regime is on the threshold of acquiring weapons of mass destruction and regularly threatens the annihilation of another UN member. In such a context, the distinction between 'imminent' and 'actualized' threat breaks down. If Israel were to wait for an attack to become fully 'imminent' in the classic sense, it would likely lose the ability to act at all, rendering the state's right of self-defence meaningless. When compliance with the existing rules is liable to result in existential catastrophe, insisting on a rigid legalistic reading fails to serve the foundational purpose of international law—to prevent wars of aggression, but also to enable states to defend their populations against genuine, unprecedented dangers. Thus, even if the author is correct in a technical sense, I argue that the jus ad bellum framework, as currently formulated, is not fully adequate to address scenarios of existential nuclear risk.
Moreover, I respectfully disagree with the author's assessment regarding the in bello dimension. Iran is not merely a passive actor but is actively engaged in continuous hostilities against Israel through its network of proxies, such as Hezbollah and the Houthis, who launch attacks every few days – not sporadically, as the Author suggests in his comments.
Ignoring this broader and persistent pattern of conduct represents a cynical application of international humanitarian law, which was never crafted with such a protracted and asymmetric threat environment in mind.
Tamás Hoffmann says
June 13, 2025
Dear Marko,
You submit that "I think we can say that reasonable scholars and states have argued that the third position is too restrictive."
The predominant majority of developing countries (i.e. the majority of the international community) seems to prefer that third, restrictive approach. Does this mean that these countries are not reasonable?
Nicolas Boeglin says
June 13, 2025
Dear professor Milanovic
Many thanks for this post. It is quite clear that self defense of Art. 51 can be invoked after being attacked ant that international law does not accept the idea of preventive self defense actions argued by US in Iraq in 2003.
May I take the opportunity to share with you and our dear coilleagues of Ejil Talk some reflections on the timing chosen (again) by Israel in order to divert international pressure on the ongoing genocide in Gaza:
As has become customary, in order to divert international attention from the drama in Gaza, and to rally its allies when they distance themselves from Israel, after a new diplomatic failure in New York yesterday (June 12th) at UNGA, Israel opted to go and bomb nuclear sites in Iran hours later, risking an immediate or near-immediate Iranian military response. It is worth recalling that days before the start of the high-level segment of UNGA in September 2024, which was set to examine the dramatic situation in Gaza, Israel launched a military operation in Lebanon with the remote explosion of thousands of beepers on 17 September 2024, initiating a confrontation with Hezbollah beyond South Lebanon.
In the same spirit of distracting international public opinion, we can also note that hours before the ICJ read its first order on Gaza in The Hague on 26 January 2024, Israel informed the world of intelligence reports of alleged ‘links’ between officials of UNRWA and Hamas: UNRWA has since been awaiting evidence and proof in this regard. See section entitled ‘UNRWA: Claims versus facts’ in this official UNRWA link:
https://www.unrwa.org/unrwa-claims-versus-facts-2025
Incidentally, Israel's military offensive on Iran on 12 June will also force France and Saudi Arabia to suspend the summit planned for 17 June in New York on the recognition of Palestine as a State.
Yours sincerely
Nicolas Boeglin
Note: on the vote at UNGA yesterday on Gaza at UNGA, with 149 in favour, inlcuding Asutarlia Canada, Germany, Italy, UK, please find this note (in Spanish, sorry):
https://derechointernacionalcr.blogspot.com/2025/06/gaza-israel-abrumadora-votacion-en.html
Yonatan Hizmi says
June 14, 2025
I read your article with great interest, and while I appreciate your effort to explore the legal dimensions of Israel’s use of force against Iran, I feel compelled to raise a broader concern regarding the framing and moral balance of your analysis.
You present a rigorous legal examination, but the near-exclusive focus on Israel’s compliance with Article 51 of the UN Charter omits crucial context: Iran is not a neutral actor. It is a theocratic dictatorship that funds and arms terrorist groups, calls openly for the destruction of Israel, suppresses its own people violently, and pursues nuclear capabilities with hostile intent. These are not marginal details — they are central to the legitimacy and necessity of Israel's defensive actions.
By not addressing these realities, your article risks creating a false moral symmetry between a democracy under existential threat and a regime that thrives on regional destabilization. Legal objectivity is valuable, but when it selectively scrutinizes one side while remaining silent on the other’s flagrant violations, it becomes a form of implicit bias — not neutrality.
Moreover, the idea that Israel must wait for a direct, imminent strike before acting — in the face of decades of declared Iranian hostility and material threats — places impossible constraints on a country’s right to defend itself preemptively. This isn't just a legal argument; it's a moral and strategic dilemma that deserves acknowledgment.
I urge you to consider whether legal neutrality, when devoid of moral clarity, might inadvertently serve those who operate outside all norms and laws.
Marko Milanovic says
June 14, 2025
Dear Tamas,
No, that's not what this means. What it means is that both positions can reasonably be held and defended. So, reasonable people like Mike Schmitt can think there is self-defence against imminent armed attacks, and reasonable people like Mary Ellen in the comments above can also argue that no such right exists until the attack materializes.
As for what the predominant position is within developing countries, I think that's really difficult to assess. Most developing states (and indeed most states) have never taken a formal position on this issue. What the dominant position is among academics within those states would be an interesting inquiry, but one that hasn't been done.
What I can say is that this is an issue that is significantly less controversial than self-defense against non-state actors. You can see that e.g. from the formal positions that states have taken in the cyber context. While there is a lot of disagreement on non-state actors, when I last counted this about 10 states expressly endorsed some variant of anticipatory self-defense (including e.g. Brazil and Singapore), while only state expressly said no, and even that is a bit unclear (Switzerland). The Common AU position acknowledges the controversy, seems to lean towards saying no, but then reserves the matter for further study. This is freshest opinio juris, as it were. See here:
https://cyberlaw.ccdcoe.org/wiki/Self-defence
https://cyberlaw.ccdcoe.org/wiki/Use_of_force#African_Union_(2024)
William Bilek says
June 14, 2025
I don't understand the uneven application of international law, as it stands today.
You note, correctly, that "There are many public statements by various Iranian officials over the years calling, expressly or impliedly, for Israel’s destruction."
This is in direct violation of the UN Charter Chapter 1: Article 2:4
"All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations."
Why is this inarguable violation of the Charter not grounds, in itself, for anticipatory self-defence?
You state: "That kind of rhetoric, however, is mainly meant for domestic political purposes in Iran and does not, without more, directly translate to an intention of the Iranian leadership to use a nuclear weapon against Israel". That is your assumption, without basis in actual fact, and based on Israel's history since 1948, could certainly be challenged. Should your assumption (or that of anyone else) be enough for Israel to put its existence on the line?
You state: "Inflammatory, even genocidal, public statements by some Iranian officials do not suffice on their own, because they are not sufficiently probative about the intent of those Iranian officials who actually make the relevant decisions."
But here it is, again: "Iran’s Supreme Leader Ayatollah Ali Khamenei on Saturday said US President Donald Trump was lying about his intentions for the region, and once again called Israel a “cancerous tumor” that must be uprooted.'
Is that not adequate "intent" by "Iranian officials who actually make the relevant decisions"?
In the stirring words of the UNSG, "These actions did not happen in a vacuum". Israel has been FACTUALLY faced with repeated attempts to exterminate it over the last 80 years. The UN and international community have failed to intervene, or to apply international law to protect it in the past. Israel's geopolitical situation renders it particularly vulnerable to existential attack. Certainly, international law (such as it is) is not a suicide pact.
Jon Angell says
June 14, 2025
Thank you for your sober analysis, Marko. And thank you for standing up for law in our age.
First, a correction. When Russia presented their legal justification for use of force in Ukraine, they relied on self defence against Nato and remedial secession of D & L after genocidal acts had occured. (Not R2P) Ukraine itself was not the issue.
I fear a dangerous tear of the legal fabric by the manner int law is practiced by powerful states. The echo, mutatis mutandis, of Natos justification in Yugoslavia and Iraq in Russias justification in Ukraine.
The way you point out Israels violation today is not the first time they act in this manner.
I want to point out how the reaction from politicians and media outlets in "our" sphere of interest differ from the Russian use of force in Ukraine Vs Israel.
How powerful states, and allies that rely on their power, neglect to check themselves when faced with the restrictions of law is reminiscent of Ethiopia v. Italy shortly before the League of Nations collapse into WW2. Hailie Selassies speech before LoN describe what European states in practice accepted - by indifference, strategy or cowardice - before Europe stood in flames.
Bill Cox says
June 14, 2025
This is a wonderfully written article, but unfortunately it adheres to that which has been occurring in journalism and is compromising the credibility of that very important avocation: an analysis steeped in correlation and altogether missing causation. Since 1979, Iran has been announcing its determination to "wipe Israel off the face of the Earth". Since then, both presidents Bush and even Ronald Reagan; President Clinton and Barack Obama have tried to play the middle ground Iran - a country who has routinely sent murderers to Israel and to kill invited American soldiers residing in other countries. This is left out of this article's narrative, and perhaps not so intentionally, but the trajectory of Iran's policies have led to its current dilemma. When the Jews, who are the most persecuted people in human history, told the world "never again" after the World War II holocaust, they were not asking. They were telling.
Nicolas Boeglin says
June 14, 2025
Dear Professor Marko Milanovic
Many thanks for this extremely inretesting post.
It is quite clear that self defense of Art. 51 of UN CHarter can be invoked after being attacked ant that international law does not accept the idea of preventive self defense actions argued by US in Iraq in 2003 and by Israel in 1981 also in Iraq (bombing of Osirak nuclear plant).
May I take the opportunity to share with you and our dear coilleagues of Ejil Talk some reflections on the timing chosen (again) by Israel in order to divert international pressure on the ongoing genocide in Gaza:
As has become customary, in order to divert international attention from the drama in Gaza, and to rally its allies when they distance themselves from Israel, after a new diplomatic failure in New York yesterday (June 12th) at UNGA, Israel opted to go and bomb nuclear sites in Iran hours later, risking an immediate or near-immediate Iranian military response. It is worth recalling that days before the start of the high-level segment of UNGA in September 2024, which was set to examine the dramatic situation in Gaza, Israel launched a military operation in Lebanon with the remote explosion of thousands of beepers on 17 September 2024, initiating a confrontation with Hezbollah beyond South Lebanon.
In the same spirit of distracting international public opinion, we can also note that hours before the ICJ read its first order on Gaza in The Hague on 26 January 2024, Israel informed the world of intelligence reports of alleged ‘links’ between officials of UNRWA and Hamas: UNRWA has since been awaiting evidence and proof in this regard. See section entitled ‘UNRWA: Claims versus facts’ in this official UNRWA link:
https://www.unrwa.org/unrwa-claims-versus-facts-2025
Incidentally, Israel's military offensive on Iran on 12 June will also force France and Saudi Arabia to suspend the summit planned for 17 June in New York on the recognition of Palestine as a State.
Yours sincerely
Nicolas Boeglin
Note: on the vote at UNGA yesterday on Gaza at UNGA, with 149 in favour, inlcuding Asutarlia Canada, Germany, Italy, UK, please find this note (in Spanish, sorry):
https://derechointernacionalcr.blogspot.com/2025/06/gaza-israel-abrumadora-votacion-en.html
Jack Bartram says
June 15, 2025
My comment actually references another comment above (or below) mine: Yotam Dov - Iran didn't suddenly decide to attack Israel. None of the predominantly Muslim countries 'just decided one day" to attack Israel. Israel has been subjugating and oppressing The Palestinians for 70 years. Israel's shameful treatment of their Muslim brothers is the biggest reason the Muslim countries in the Middle East hate Israel.
Liron A. Libman says
June 15, 2025
Dear Marko,
Thank you for your thoughtful analysis and for your intellectual honesty in acknowledging the limits of our knowledge of the relevant facts. A robust legal analysis must be built on a solid factual foundation; without it, we are left with purely theoretical exercise.
Your article, and the insightful responses from Olivia, Ori, and Marty, clarify that the central point of legal disagreement is the relevance of the ongoing armed conflict between Israel and Iran. While you argue this is not relevant to the jus ad bellum analysis—maintaining that an escalation requires the same necessity and proportionality justification as a first strike—others differ. To the authorities supporting this latter view, I would add the late Professor Yoram Dinstein and a 2016 White House report (from President Obama's term), that I cited in my Lawfare piece on prior Iranian threats: https://www.lawfaremedia.org/article/does-haniyeh-s-death-give-iran-the-right-to-attack-israel
I concur that justifying the recent Israeli action as a standalone pre-emptive strike is challenging, particularly from a formalist-positivist perspective. However, a comprehensive legal assessment must incorporate several additional facts:
1. A Coordinated Plan of Attack: Captured Hamas documents indicate an Iranian-led strategic plan to annihilate Israel through a coordinated, multi-front attack by its proxies. This evidence points to a threat far more concrete than mere "rhetoric… meant for domestic political purposes." See: https://www.terrorism-info.org.il/en/hamas-strategy-to-destroy-israel-from-theory-into-practice-as-seen-in-captured-documents/
2. The Threat of Nuclear Possession: The analysis should not be limited to the threat of Iran’s imminent use of a nuclear weapon. The strategic threat of Iran’s mere possession of one—which could provide a nuclear shield for a large-scale imminent conventional attack—must also be considered.
3. Israel’s Unique Geopolitical Vulnerability: There is a profound asymmetry between the two states. Iran is over seventy times larger than Israel, whose population, industry, and government are concentrated in a small area. The statement "Israel is a one-bomb state," attributed to former Iranian president Rafsanjani, underscores why Cold War theories of mutual deterrence are inapplicable (even assuming Israel has nuclear weapons). See: https://www.fdd.org/podcasts/2025/05/21/going-ballistic-inside-irans-military-strategy-and-arsenal/ ; https://www.aei.org/foreign-and-defense-policy/middle-east/what-would-one-big-nuke-do-to-israel-this/ ; https://www.cia.gov/the-world-factbook/middle-east/
4. Exhaustion of Non-Forcible Alternatives: The diplomatic track appeared exhausted. A day before the Israeli attack, the IAEA reported it could not verify the absence of nuclear material diversion or provide assurance that Iran's program was "exclusively peaceful." Iran’s defiant response—announcing a new enrichment facility and installing advanced centrifuges at its underground Fordo site—signaled a rejection of meaningful negotiations. See: https://www.bbc.com/news/articles/ce3v6w2qr12o
Furthermore, President Trump explicitly gave Iran 60 days to reach an agreement and the attack was on day 61, see: https://www.reuters.com/world/middle-east/trump-tells-reuters-its-unclear-if-iran-still-has-nuclear-program-2025-06-13/
Finally, even if one concludes that Israel's attack was contrary to international law, we are faced with a stark policy choice. This situation brings to mind the saying that "international law is not a suicide pact." While broadening the interpretation of self-defense carries a systemic risk of encouraging escalation, the present case poses a specific, existential risk: missing the last opportunity to prevent a fanatical regime, openly committed to Israel's destruction, from acquiring the ultimate means to achieve that end.
For those of us who are the direct targets of that regime, the choice is clear. It's fair to ask whether those who don't bear the consequences of miscalculation should be the ultimate arbiters of that risk.
Thank you again for prompting this vital discussion.
Guy Prado says
June 15, 2025
Dear Marko,
I would be grateful if you could address some of the recent contentions put forward by Professor Louis René Beres, as published through the Begin-Sadat Center for Strategic Studies. Beres thoroughly examines the nature behind "the right of anticipatory self-defense" and its applications in recent Israeli military operations against Iran. He argues in benefit of anticipatory self-defense, demonstrating how it is a well-established legal norm, and poses an interesting argument based on the Genocide Convention. According to his reading, this threat activates not only Israel's right under customary international law to engage in anticipatory self-defense, but also imposes a legal duty to prevent genocide.
Marty Lederman says
June 15, 2025
Amichai Cohen and Yuval Shany offer some very thoughtful and thought-provoking reactions to the IAC/ad bellum/proportionality questions we've been engaging here.
https://www.justsecurity.org/114641/israel-iran-un-charter-jus-ad-bellum/
Nicolas Boeglin says
June 15, 2025
Dear Professor Milanovic
May I add to my previous message on the Israel´s strategy to divert international public opinion of the ongoing genocide in Gaza, this leaked email concerning Collin Powell US former State Secretary:
"in an email he sent to US Democratic party donor Jeffrey Leeds, Powell wrote that he doubted the Iranian regime would use an atomic bomb even if it could get one, since “the boys in Tehran know Israel has 200, all targeted on Tehran, and we have thousands.”
Source:
https://www.timesofisrael.com/in-leaked-emails-colin-powell-says-israel-has-200-nukes/
Considering some comments read referring to the "absolute existential threat" of Iranian nuclear programme for Israel, I think this leaked email can help to understand better Israel´s real strategy since last June 12.
Yours sincerely
Nicolas Boeglin