The Illegal Israeli-American Use of Force Against Iran: A Follow-Up

Yesterday, the United States joined Israel in its use of force against Iran by conducting a precision bombing operation targeting Iranian nuclear sites. Like Israel’s use of force before it, this use of force by the United States is, in my view, quite clearly illegal – a breach of the prohibition on the use of force in Article 2(4) of the UN Charter. This is simply because the legality of the US use of force is parasitic on the validity of Israel’s arguments justifying its use of force.

In this post, I will discuss some issues concerning the legal position of third states with respect to this use of force against Iran. I will first revisit some of the arguments relating to Israel’s use of force, then discuss America’s involvement, then turn to the question whether states exercising their right to self-defence can lawfully violate the airspace of third states, and then finally talk about whether third states can assist Israel in shooting down Iranian missiles.

No Imminent Nuclear Armed Attack Against Israel

As I explained in my previous post, the only viable argument that Israel has to justify its use of force against Iran is anticipatory self-defence. That is, it would have to be necessary to act forcefully today to stop an imminent nuclear armed attack by Iran against Israel. The basic problem for Israel’s position is a factual one. Even on very flexible understandings of imminence, it cannot be argued, on the evidence that is currently publicly available, that (1) Iran has decided to build a nuclear weapon, i.e. that its leadership intends to do so, and that (2) once the weapon is built, Iran intends to use it against Israel.

To be clear, this does not mean that Iran’s nuclear programme is a peaceful one.  It obviously isn’t. Iran would not need the facilities it built, or the amount of highly enriched uranium that it has, just for a peaceful nuclear energy programme. What Iran clearly wanted was to have the option of building an atomic bomb relatively quickly, an option its leadership regarded as essential for preserving their regime. Their pursuance of that option has also led to the current situation. But simply pursuing that option, while undoubtedly posing a threat to Israel and to the wider region, does not translate to an imminent armed attack, even on broader, non-temporal understanding of imminence.

Recent reporting confirms this assessment. A New York Times article from a few days ago, relying heavily on US intelligence sources, noted that:

U.S. intelligence agencies continue to believe that Iran has yet to decide whether to make a nuclear bomb even though it has developed a large stockpile of the enriched uranium necessary for it to do so, according to intelligence and other American officials.

That assessment has not changed since the intelligence agencies last addressed the question of Iran’s intentions in March, the officials said, even as Israel has attacked Iranian nuclear facilities.

The article also noted that Israeli intelligence agencies did not provide their US counterparts with new evidence that could change this assessment, despite arguing that Iran could produce a weapon much more quickly than previously assessed. Rather, ‘officials said that information from Israel and other sources was not new intelligence about the program or Iranian intent to build a bomb, but rather new analysis of existing work.’ Shades of Iraq 2003 is all that needs to be said here.

So, again, of the two intents/decisions noted above – building a weapon and using it against Israel – there is insufficient evidence even of the former, let alone of the latter. Whether that assessment will change after the US attack on Iranian nuclear facilities is a different matter.

Arguments Justifying Israel’s Use of Force

In addition to various points made in the comments to my first post, several articles have been published by colleagues attempting to justify Israel’s use of force against Iran (see Cohen and Shany; Schmitt; Corn and Kittrie; Tsagourias ; but see Haque, for a blow-by-blow response to some of these arguments). More importantly, Israel has also articulated its official justification for its use of force in a letter to the Security Council – and this is the justification that counts.

Broadly speaking, there are three arguments that have been used to justify Israel’s use of force:

1. That it was part of an ongoing international armed conflict between Israel and Iran, which obviates the need for any further ad bellum analysis (see Corn and Kittrie in particular);
2. That there was an ongoing armed attack by Iran against Israel, and that Israel’s use of force is a response to that attack, while remaining necessary and proportionate to stop that attack (see Cohen and Shany in particular)
3. That there was, in fact, an imminent nuclear armed attack by Iran against Israel, and that the military response was necessary and proportionate because this was the last window of opportunity in which Israel could act (again, Corn and Kittrie, but also Schmitt).

All of these arguments are echoed in Israel’s own letter, without clear differentiation between them. On the contrary, they are deliberately mushed together, as are political and legal justifications. None of them are persuasive. (Indeed, whenever one sees a potpourri of different arguments being used to justify a use of force, this is generally a very reliable indicator that the arguments taken individually are weak. Putting them together doesn’t make them any stronger – see, e.g., the 2003 invasion of Iraq, or the 2022 invasion of Ukraine.)

As for the first argument, it rests on the academic work of the late Yoram Dinstein and his rather idiosyncratic approach to the relevance of the notion of ‘war’ in the modern jus ad bellum. The argument essentially conflates the ad bellum with the in bello. Here I only need to quote from Mike Schmitt’s post cited above:

Although a Dinstein analysis should never be easily dismissed, I do not share his understanding In this case (see also Milanovic). Instead, I support the view preferred by most experts, according to which the jus ad bellum and the law of armed conflict are distinct bodies of law (see also Sassoli and Mačák) that apply in tandem.

I am not suggesting that every operation must be independently assessed against the self-defense criteria; such a standard would be operationally unworkable. Indeed, so long as future operations are reasonably foreseeable and hostilities have been relatively uninterrupted, there is a continuing right of self-defense. And the very existence of hostilities can bolster the case for satisfaction of the anticipatory self-defense criteria discussed above. But when a significant shift in the nature of the conflict occurs, as is the case with the targeting of Iran’s nuclear assets following a relative lull in the fighting, it is appropriate to reassess whether there is a basis for that particular use of force and whether it complies with the conditions of proportionality and necessity (see also Greenwood, p. 223).

To this I would only add that the ICJ’s 2024 advisory opinion on the occupation of Palestinian territories very much supports the proposition that an ad bellum self-defence assessment is a continuing one, not one that is done only at the moment an armed conflict arises (see more Milanovic, ‘The Notion of an Illegal Occupation in the ICJ’s Palestine Advisory Opinion,’ ICLQ (forthcoming)).

As for the second argument – that Israel was subject to an ongoing armed attack by Iran in the sense of Article 51 of the Charter – I would simply reiterate the points I made in the comments discussion to my original post. Frankly it defies even common sense to say that on, say, 11 or 12 June, Iran was attacking Israel. On the contrary, as Cohen and Shany themselves say in the opening of their post cited above, it was Israel that attacked Iran on 13 June. This is just reality. Even if there was an ongoing attack by Iran against Israel, it was one of such low intensity that the response we see now could not satisfy any reasonable conception of necessity and proportionality. Those who argue otherwise would, I imagine, also consider that a few weeks ago India or Pakistan (depending on who you think started that conflict) would have had the right, while acting in self-defence, to attack the nuclear programme of their adversary. This is an argument that essentially renders any necessity/proportionality analysis meaningless.

This leaves us with the third argument, which is about imminence. We all agree that this assessment depends on the prior context. Here I want to make two points, mainly in response to Mike. The first relates to the various hostile statements made by Iranian officials against Israel – here Mike argues that ‘if there is a degree of uncertainty as to whether Iranian leaders mean what they say, the risk of being wrong should be shouldered by the side making the threatening statement.’  

This position is problematic for several reasons. First, because Iranian officials have said many things, including that they are not pursuing a nuclear weapon – and it is unclear why only some of their statements are probative of their real intent. Second, because Israeli officials have over the years said many inflammatory things as well – e.g., very recently, that ‘Tehran will burn.’ And I do wonder, with the record of extreme statements by Israeli officials regarding Gaza in particular, whether it is in the best interest of the State of Israel to adopt a legal principle by which all of those statements should be taken literally (which, I note, Amichai and Yuval have previously argued against.) Finally, and most importantly, there is evidence other than statements that is probative of a state’s intent. Israel has shown many times how it has been able to effectively spy on Iran’s leaders, yet, as the New York Times article referred to above notes, it hasn’t been able to persuade even the US intelligence community that Iran has committed itself to building a bomb, let alone to using it against Israel.

So, bottom line – all of these arguments are really trying to dress up purely preventative action into something more legally respectable. These arguments are not just weak, they are fatally weak (something that Mike, with his usual talent for understatement, acknowledges when he says that the anticipatory self-defence argument is colourable or reasonable while requiring liberal interpretation of various elements in question.)

Are International Law Experts Divided?

A good explainer for a lay audience in the New York Times noted that international law experts are divided on the legality of Israel’s use of force. Judging from the articles that have appeared in the past few days, that seems – at first glance – to be the correct assessment. But, with the greatest respect to the colleagues who disagree, the divide is actually not so great. Since I am happily not on social media, and never will be, I have no idea what the assembled international law commentariat said there – but from what I hear I’m pretty sure the majority view is that Israel has acted unlawfully. And sure, it’s always a problem in our line of work to reliably establish what the majority position on some issues is, and we’re not dealing with a hard science here anyway.

What I would say, however, entirely from my own sense of the mainstream in our profession and the discussions I’ve had in recent days, is that more than 90% of international law experts regard Israel’s attack on Iran as unlawful. I’m pretty sure of that, for whatever that anecdotal evidence is worth. I am also sure that, were this issue to come before the International Court of Justice, say in advisory proceedings, a great majority of the Court’s judges (maybe even 14 to 1…) would say that Israel has used force unlawfully. I am also sure that if, say, the American Society of International Law or the European Society of International Law polled their members, or did a hand count at a conference, we would again have overwhelming majorities condemning this use of force as unlawful. (It would be nice if someone actually did this! I did do this once as a moderator at an ESIL conference many years ago with regard to the 2003 invasion of Iraq, and the result was – if memory serves – that one person in the room thought that the invasion was legal.)

So no, despite all of the reasonable, colourable, plausible or whatever arguments being made, this is not a tough case. To paraphrase an infamous quote, the best case in favour of Israel’s potpourri of arguments justifying its use of force against Iran is that it cannot be said to be unambiguously illegal.

But we all know it’s illegal. Just like we did with Iraq in 2003 or Ukraine in 2022. And any ambiguity here is entirely due to decades of efforts by the states concerned, some of their government lawyers, and some academic lawyers, to generate as much flexibility in the existing rules as possible. Whether this is a good thing or a bad thing is a matter of perspective. But there should be no doubt that whatever ambiguity exists here was generated deliberately so that it could be exploited. There should also be no doubt that such efforts are in tension with the overarching purpose of the Charter system, which is to minimize unilateral resort to force.

Or, if I can put it this way, some of the legal arguments being used to justify Israel’s action against Iran are exactly the same as those used by Russia to justify invading Ukraine. The difference is in the facts. I cannot help but remember here the front page of the most horrible of all pro-government tabloids in Serbia, published on the eve of Russia’s wholescale invasion, which read ‘Ukraine attacks Russia!’

That, quite simply, is what this argument boils down to. It is the literal inversion of reality. Again, I do acknowledge that Israel has far more valid reasons to be concerned about a nuclear-armed Iran than Russia had about hypothetical future attacks from Ukraine. But the core legal argument is the same. It is identical in its unboundedness, in its ability to completely hollow out the legal prohibition on the use of force in international relations. As far as I’m concerned, as an international lawyer I’d much rather stand with an Elizabeth Wilmshurst than create corrosive apologies for the use of force that other states, like Putin’s Russia, could easily exploit in the future. Maybe – maybe – the Israeli-American military adventure against Iran will lead to good outcomes. I have no way of knowing that, but I accept that there is a possible good case scenario out there. But there are many catastrophic ways in which this could turn out as well, and international law at least is clear in how it assesses the various risks at play.

Have Third States Accepted the Validity of Israel’s Arguments?

What international lawyers may think is one thing. But it is states who make international law – and it is therefore important to consider, now and in the months to follow, what exactly they have said or will say about Israel’s justification for using force against Iran. As things stand, I find two points particularly striking. The first is that even the closest allies of Israel and the US have used carefully crafted language which, on the one hand, provided political support for their allies, but, on the other hand, avoided endorsing their legal arguments. So, for example, the statement of the leaders assembled at the recent G7 meeting affirmed ‘that Israel has a right to defend itself,’ but did not say that this particular use of force was justified by self-defence. By contrast, the 57 member states of the Organisation of Islamic Cooperation clearly labelled Israel’s strikes against Iran as aggression.

The second point is that I am reasonably certain that – to the extent they are being consulted – the government lawyers in many Western governments are advising their leaders that Israel’s actions are unlawful. This has clearly happened in the UK – the Attorney-General, Lord Hermer, has reportedly provided some kind of preliminary advice to the effect that he would have ‘concerns about the UK playing any role in this except for defending our allies.’  This meant, inter alia, that the US did not even ask the UK to use the Diego Garcia airbase to launch the strikes against Iran – we will of course see how this will unfold in the days to come.

Thus, we can observe how Western states are understandably keen not to antagonize the Trump administration too much, while calling for restraint and de-escalation and politically blaming Iran for much of what has happened. Yet, at the same time, none have clearly come out with a legal position endorsing the Israeli use of force. And at least some of their government lawyers – and maybe a great many – are standing with Wilmshurst, if I can put it that way. 

Collective Self-Defence as the Only Viable Argument for the United States

What then of the legality of US airstrikes? The only viable argument that the US could make here is one of collective self-defence of Israel, at Israel’s request. Thus, the whole ‘self-defence is irrelevant during an ongoing armed conflict’ point – which, as explained above, is incorrect even when it pertains solely to Israel – makes no sense if the US wishes to justify its own use of force. It is difficult to see how the US could plausibly argue that Iran would imminently attack America. So the only claim available is that Israel is defending itself, and that the US is helping it do so, within the bounds of necessity and proportionality.

This is precisely the argument that the US representative made at yesterday’s emergency session of the Security Council: ‘This operation sought to eliminate a longstanding but rapidly escalating source of global insecurity, and to aid our ally Israel in our inherent right of collective self-defense consistent with the UN Charter.’

The validity of this argument is entirely parasitic on any Israeli claim to self-defence under Article 51 of the Charter. If I am wrong, and those lawyers justifying Israel’s actions are right, that Israel is exercising self-defence, then the US would have the right to assist it. Its military actions so far, which seem to be strictly limited to Iran’s nuclear programme, would also comply with necessity and proportionality. Regime change, however, would be out of bounds even on these assumptions. But if I am right that Israel is acting unlawfully, then the US would have no right to collective self-defence either – just like, for example, Iran or North Korea could not rely on collective self-defence to justify their assistance to Russia against Ukraine. In that same vein, the UK or other US allies would have no right to join any further use of force against Iran, including through the provision of airfields, weapons or refuelling, absent some major change in circumstances.

Self-Defence and Overflight

Aside from simply reacting to the use of force between Israel, America and Iran, some states in the region are more directly affected because the parties to the conflict are using their airspace to conduct hostilities against each other. Thus, Israel has repeatedly violated Iraqi airspace so that it combat aircraft could reach Iran, and Iraq has protested this as a violation of its sovereignty. Yesterday’s US B-2s strikes also used Iraqi airspace, although Iraq has not protested (yet). Jordan has shot down Iranian drones and cruise missiles, while Saudi Arabia seems to have allowed Israel to use its airspace to shoot down incoming Iranian ordinance. (Readers will correct me if I am wrong, but most Iranian ballistic missiles would likely not violate the airspace of any other state, because of their steep suborbital trajectory).

This raises two important questions of principle. First, can a state exercising self-defence (which for the sake of the argument can here be either Iran or Israel) use the airspace of another state, without that state’s consent, if this is the only way in which it could reach its adversary – in other words, if it was strictly necessary to do so? This would depend on whether we conceive of self-defence as a right that is opposable to third parties, not simply the attacking state. Or, put differently, the issue is whether self-defence can operate as a circumstance precluding the wrongfulness of the violation of the rights of third states, such as their territorial sovereignty.

From what I can tell (but I have not done in-depth research on this point, and am grateful for any references that readers might have), there is no consensus on this point either in state practice or in the literature. In its commentary to Article 21 of the Articles on State Responsibility, at para 5, the ILC left completely open what the effect of self-defence could be vis-à-vis third states, but in doing so it clearly contemplated that such an effect could exist (‘Article 21 leaves open all issues of the effect of action in self-defence vis-à-vis third States.’). Thus, to the extent that there is no use of force against the third state, but simply overflight that can be categorized as a trespass breaching its sovereignty, self-defence could potentially be used to preclude the wrongfulness of that violation. This is also the view of the colleagues with whom I’ve corresponded on the matter – but it is somewhat tentative. The one point on which I am certain, however, is that the answer to this question cannot be found in the law of neutrality (which should die, if it is not dead already). An aggressor state would obviously have no right to violate the airspace of third states.

The second question of principle is whether the transit state has any right to use force against the aircraft or ordinance of the state claiming self-defence. That is, if Iran’s firing of drones or missiles against Israel is an act of self-defence (which it is), can Jordan shoot them down? One view, likely the better one, would be that there is no self-defence against self-defence. Thus, if Israel or the US are exercising the right to individual and collective self-defence against Iran, and it is necessary for them to breach Iraqi airspace to do so, Iraq would have no right to use force to prevent them from doing so. Another view would be that self-defence precludes wrongfulness, but that Iraq could still respond to a breach of its sovereignty, i.e. that Iraq or Jordan would not be bound to tolerate breaches of their airspace.

Self-Defence Against Unnecessary or Disproportionate Self-Defence

This brings me to the final, related issue I want to examine. Putting aside yesterday’s strikes for a moment, is the US entitled to assist Israel to shoot down incoming Iranian missiles, as it has done, even if it is Iran that is exercising its right to self-defence? Again, on the strict view that no self-defence is available against self-defence, such assistance would be unlawful – even if the failure to provide such assistance would mean that some Israeli civilians would undoubtedly die or be harmed in Iranian missile strikes.

An alternative view would be that third states could be justified in shooting down Iranian missiles to the extent those strikes constitute an unnecessary or disproportionate exercise of self-defence on Iran’s behalf. In other words, while there is no self-defence against self-defence, there is self-defence against self-defence which exceeds its permitted bounds. As Mike Schmitt has put it:

There is generally no right, individual or collective, to defend against actions undertaken pursuant to the jus ad bellum right of self-defense. Nevertheless, if reports that Iran is targeting population centers in addition to military targets are accurate, the United States is entitled to help Israel defend against them, for unlawful actions (targeting civilians and civilian objects in violation of LOAC) do not satisfy the necessity criterion of self-defense and therefore are themselves unlawful uses of force (armed attacks) triggering the right of individual and collective self-defense. Obviously, the analysis of the current situation is highly fact dependent.

I think this is right. The key problem is one of fact, as Mike points out. While some Iranian missiles have hit civilian objects, this does not mean that they were necessarily targeted against these objects, or that they were fired indiscriminately. There are also plenty of examples of Iranian missiles hitting military objectives in Israel, or very close to them. This would therefore pose a major difficulty for any third state seeking to protect Israel from incoming missile fire – how could it know whether the incoming fire is directed against civilians or is indiscriminate, and is therefore not necessary and proportionate in ad bellum terms? Unless some kind of overall assessment can be made of how Iran has directed its missile strikes – and this is a question for military experts – it is difficult to see how this assessment can be made on a case-by-case basis for ballistic missiles which spend around ten minutes in flight.

Conclusion

To summarize:

1. No evidence has come to light supporting the view that there was an imminent nuclear armed attack by Iran against Israel. No other argument can support Israel’s use of force.
2. Israel’s use of force is therefore illegal. And, again with greatest respect to colleagues who think differently, this is not a close, tough or hard case. The assessment would be different only if information came to light that clearly indicated that Iran did decide to make a nuclear bomb and did decide to use it against Israel – the public statements by Iranian officials simply do not qualify as such. None of them have said that they are building a bomb, or that they would use it against Israel.
3. The use of force by the United States against Iran is also illegal, since it cannot be justified as the collective self-defence of Israel.
4. Third states have a legal obligation to refrain from providing aid and assistance to unlawful uses of force.
5. It is likely justified for a state exercising its right to self-defence to violate the airspace of a third state, if doing so was the only way of effectively exercising self-defence against its adversary, the aggressor state.
6. It is likely justified for third states to assist Israel in deflecting Iranian missiles, but only if there was evidence, either generally or specifically, that Iranian missile strikes exceed the necessity and proportionality criteria of self-defence.

(Administrative note: I am with family on holiday in South East Asia, and wrote this in a few hours by the pool. Apologies for any errors. Apologies also if I fail to engage with the comments, as I normally would.)