Iran Unlawfully Retaliates Against the United States, Violating Iraqi Sovereignty in the Process

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Today Iran launched a number of ballistic missiles against two US military bases in Iraq, in response to the US strike on Soleimani last week. As of now it is unclear whether the missiles caused any American or Iraqi casualties. Donald Trump will address the public in this regard in the morning today US time.

Hopefully there will be no further escalation of hostilities after this Iranian missile strike. It is crystal clear, however, that the strike was unlawful. It breached the prohibition on the use of force in Article 2(4) of the UN Charter with respect to both the United States and Iraq. It did so because of its purely retaliatory nature.

The Iranian Foreign Minister, Javad Zarif, gave Iran’s public justification for the strike on Twitter:

Note his explicit reliance on self-defence per Article 51 of the Charter, the reference to proportionality, and to Iran having concluded its defensive action. Clearly this is meant to say that Iran intends to take no further action (at least not openly) if the US for its part refrains from further hostilities. Again, let’s hope that such de-escalation actually happens. That said, however carefully framed, Zarif’s invocation of self-defence is still incapable of legally justifying Iran’s actions.

Let’s assume that the US strike on Soleimani was an unlawful use of force against Iran, as I argued that it most likely was. Let’s assume further that it was also an armed attack in the sense of Article 51 of the Charter (i.e. under the majority view, including that of the ICJ, a more serious and grave form of unlawful force), which would in principle entitle Iran to take measures in self-defence. Let’s also assume that the killing of Soleimani was in fact executed from the two US bases that Iran has now struck. Even if all of this is true, the basic problem for Iran is that the US strike on Soleimani was completed. Because that attack was over, there could be no necessity to act to repel it. It is only if Iran could argue on the facts that it anticipated future imminent attacks by the US that it could plausibly have a claim to self-defence, and Zarif mentioned no such attacks.

In other words, the only legal theory that Iran could reasonably rely on is the one that the US had previously used against it. Relying on such a theory would of course implicitly validate the US position, on the law if not on the facts, which is presumably why the Foreign Minister avoided using terms such as imminence. But that does not change the fact that the Charter does not permit any use of force, however otherwise proportionate, which is purely retaliatory in nature. And we know it was retaliatory not only because the armed attack which precipitated was over, but also because other Iranian leaders have repeatedly said so – in fact, Ayatollah Khamenei decided that the retaliation for Soleimani’s killing must be done openly by regular Iranian forces, as they have now done.

It is now also unambiguously clear that, as a matter of international humanitarian law, an international armed conflict (IAC) exists between the US and Iran. According to the Pictet Commentary on the Geneva Conventions, a position reaffirmed in the new ICRC commentary (para 236):

Any difference arising between two States and leading to the intervention of armed forces is an armed conflict within the meaning of Article 2, even if one of the Parties denies the existence of a state of war. It makes no difference how long the conflict lasts, or how much slaughter takes place. The respect due to the human person as such is not measured by the number of victims.

It is also perfectly possible that the IAC preceded Soleimani’s killing, for example due to fighting between the US and Iranian proxies in Iraq. To the extent that IHL applied, both the killing of Soleimani and the Iranian missile strike in response were lawful, since the attacks were directed at combatants and military objects, in compliance with the principle of distinction.

This does not, however, obviate the need for compliance with the jus ad bellum. The fact that an IAC exists today (but will hopefully imminently end) between the two states does not license either of them to escalate hostilities further. This, again, is an ad bellum question, especially in light of the fact that the hostilities to date have taken place on the territory of a third state, Iraq. It will be interesting to observe in the next few days whether the Iraqi government will protest the violation of its sovereignty by Iran with the same vigour with which it protested the equivalent violation by the United States. It is also interesting to observe (although regrettably this is not exactly uncommon) how both the US and Iran have had to resort to the language of international law to legitimize their actions externally, without actually complying with what the law requires.

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Parisa Zangeneh says

January 8, 2020

With the impeachment hearings and the next presidential election looming, let’s also hope that this ends quickly and doesn’t serve as a distraction from reality, as well as a rallying point for President Trump.

Brian McGarry says

January 8, 2020

Thanks for this Marko. On the territorial aspect that you end with: it could be interesting to draw analogy to another instance where a State formally claimed Art 51 individual self-defence in response to an armed attack taking place abroad...

Farshad Kashani says

January 8, 2020

Hi Marko,

I understood the legal saturation as and armed conflict, different.
The US shot Iraqi and Iranian high rank military official in Iraq territory without any record of armed conflict at that time.
1.It is violation Iraqi sovereignty by the US.

2.The US shot and used armed attack against an Iranian whom was not immediate threat and started International Armed Conflict.

3.The targeted officials killed by the US which is not only disproportionate act by the striker but also is arbitrary act and an extrajudicial execution.

4.In response to the US drone strike against slain official, Iran concluded proportionate measures in self-defense under UN Charter article 51 and considered IHL by attaching military bases target instead of militant (s).

5.The issue have declared by the country to the UNSC and explained that that took self-defense and dense not seek escalation or war.

Hoping for peace,

Farshad Kashani says

January 8, 2020

Apologize for the typing mistake. Unfortunately there is no chance for editing

DeQuincey says

January 8, 2020

Interesting selective approach to illegality given that the US invaded and occupied Iraq, and Australia claims (and has refused to present evidence) that they were invited to participate in the coalition by Iraq (something Iraq denies).

Would you like to address Trump's repeated public threats to destroy Iranian cultural sites? That is a crime on a number of counts.

Marko Milanovic says

January 8, 2020

Hi Farshad,

As I explained in my post, the legality of the actions of both the US and Iran under IHL/the jus in bello has nothing to do with their legality under the jus ad bellum. In particular, Iran's response was unlawful because the attack it responded to was already over, and accordingly there was no necessity to respond. See more in that regard Adil Haque's excellent post on Just Security, providing extensive quotes from Iran's own arguments before the International Court of Justice which explain that no necessity exists for attacks that are already over:

DeQuincey, I'm not sure what selectivity exactly you see here - and I did indeed address Trump's illegal threats in my post from yesterday. The US invasion Iraq in 2003 was unlawful, but that is legally irrelevant with respect to assessing the events of the past week.

Jack McDonald says

January 8, 2020

I'm interested in your view regarding jus ad bellum as a constraint on an existing IAC. If an IAC between the US and Iran were conducted on their own territory, or in international waters, would your view that jus ad bellum concerns limit escalation still hold? Or is it your view that jus ad bellum constrains IAC escalation on third party territory only?

Another Humble Visitor says

January 8, 2020

Dear Marko,

Thank you for sharing your comments on the most recent incidents between US and Iran.

Agreeing that the killing of Soleimani by the US and hitting of US bases by Iran are both unlawful in the context of self-defence, I would also like to draw attention to two things on the selectivity that was brought by DeQuincey.

First, your headlines and I quote:

"The Soleimani Strike and Self-Defence Against an Imminent Armed Attack"

"Iran Unlawfully Retaliates Against the United States, Violating Iraqi Sovereignty in the Process"

Even though you conclude that the killing of Soleimani was unlawful, you choose not to reflect it in your first headline, while you clearly put the word "unlawful" for the second headline.

Second, you say:

"It is also perfectly possible that the IAC preceded Soleimani’s killing, for example due to fighting between the US and Iranian proxies in Iraq. To the extent that IHL applied, both the killing of Soleimani and the Iranian missile strike in response were lawful, since the attacks were directed at combatants and military objects, in compliance with the principle of distinction."

Following this line of argument, one expects to hear a few sentences regarding the legality of the Iranian action under the IHL. While you try to demonstrate the US may perfectly rely on the existence of armed conflict that makes the killing of Soleimani lawful, you do not seem to bother to apply the same for the Iranian action. Iran may also rely on IHL that makes the hitting of the base lawful. There is also a possibility, under your arguments, that the Iranian action may be lawful. This fact, however, is completely excluded in your heading for the Iranian action and further analyses.

It makes me think that we, as international lawyers, seem to try hard to find a US action "legal" by addressing a lot of scenarios, while we are ready too ready to call the actions of weaker states "unlawful".


Marko Milanovic says

January 8, 2020

Another Visitor, I genuinely don't see any selectivity or bias in how I framed the titles of the two posts. Each time I tried to capture what the main thrust of the post would be, and the first one focuses extensively on imminence. And as I explained in the first there is some complexity in whether the US strike against Soleimani can be justified in self-defence, whereas the illegality of the Iranian missile strike is straightforward.

On your second point re IHL, I said expressly that: 'To the extent that IHL applied, both the killing of Soleimani and the Iranian missile strike in response were lawful, since the attacks were directed at combatants and military objects, in compliance with the principle of distinction.' The complex issue here is when the IAC exactly started. The choice of target is generally not - well, let me qualify that, because on the one hand the US strike killed more people than just Soleimani, while the Iranian strike endangered soldiers from other states (e.g. Slovenia) stationed in the base and potentially Iraqi bystanders as well.

But again, as I explained above, the fact that under IHL Iran is perfectly entitled to send missiles against a US military base doesn't mean it is allowed to do that by the Charter-based jus ad bellum. The applicability of IHL doesn't displace a self-defence analysis.

So, to sum up, I really think the implication that I am somehow biased pro-US (strong) and anti-Iran (weak) is unfounded. The fact that the analysis re the Iranian strike is simple is because, as I explained it, it is elementary that self-defence cannot be punitive. Such was also precisely the view of Iran's counsel before the ICJ in the Oil Platforms case, which Adil extensively quotes. The issue of self-defence against imminent attacks is much more complex. Had Iran invoked such a theory, the lawfulness of its strike would have been more arguable, or at least factually contingent in the way the US argument is.

Leila sadat says

January 8, 2020

I very much appreciate both comments Marko. Here are my thoughts about the U.S. strike. I would love your response. Happy to take it off-line.

Mary Ellen O'Connell says

January 8, 2020

Dear Marko,

I concur that the jus ad bellum prohibits reprisals of the type Iran has launched against U.S. bases in Iraq. Adil Haque's post at JustSecurity on this is excellent as you indicate. My own post of January 5 also states that Iran would have no right to resort to military force following the the Soleimani killing:

For more on the illegality of reprisals, readers might find this post helpful:

That said, like Jack, I am puzzled by your IAC point. You rightly emphasize that the U.S. and Iranian attacks are now "completed" or "concluded". So why is there an IAC now? You suggest it might have existed when Soleimani was assassinated because of the Iranian-backed militia attacks on U.S. personnel but you seem unsure. Why didn't it begin when Iran and the U.S. shot down each other's drones in June and July?

That is the problem with the Pictet comment. Perhaps it is positive if a state determined to violate the prohibition on the use of force at least targets military rather than civilian targets. But states should never believe that following IHL justifies a first use of military force. That is the problem of suggesting that IHL applies in the absence of an actual armed conflict. The first use of force is always unlawful whether it begins with an attack on a military or civilian site and regardless of whether it is followed by fighting that meets the definition of armed conflict.

See the thorough research on these points in ILA Committee on the Use of Force, ‘Final Report on the Meaning of Armed Conflict under International Law’ (2010).


Mary Ellen

Yet another humble visitor says

January 9, 2020

Just to complement "another humble visitor" above and react to these conclusions by the author: "So, to sum up, I really think the implication that I am somehow biased pro-US (strong) and anti-Iran (weak) is unfounded. The fact that the analysis re the Iranian strike is simple is because, as I explained it, it is elementary that self-defence cannot be punitive." "It is only if Iran could argue on the facts that it anticipated future imminent attacks by the US that it could plausibly have a claim to self-defence, and Zarif mentioned no such attacks."

Does it mean that if Zarif mentioned (without adducing any further evidence) that the attacks were directed against future imminent US attacks against Iran, the second headline would read:

“The Iranian Strike and Self-Defence Against an Imminent Armed Attack”?

And the conclusion would be that "Be that as it may, the remainder of this discussion will proceed on the assumption that Iran could conceivably provide such a justification."?

Thanks as well.

Dr Abdulaziz Alkhtabi says

January 9, 2020

Dear Mr Marke
We can research about legality of these operations under the title of reprisals with comparism of Article 51 requirements

Marko Milanovic says

January 9, 2020


Apologies for not having seen your comment earlier. Yes, my view is that the jus ad bellum would constrain escalation even for actions that did not take place on the territory of a third state, such as Iraq. The fact that an IAC exists (or existed) doesn't mean that the US is entitled to engage in a full-scale bombing campaign of targets in Iran, or that Iran would be entitled to fire missiles at US aircraft carriers on the high seas. Again, this follows from the basic principle that the purpose behind defensive action must not be punitive.

Thanks Leila for your comment, very much endorse your article.

Mary Ellen, it is perfectly possible that an Iran-US IAC existed at some point before, but then petered out. Nothing much really depends on it. Again I just don't agree that accepting the applicability of IHL somehow enables escalation - the jus ad bellum constrains that.

Yet another visitor,

I have no idea what the title of my second post would have been had Iran endorsed an imminence theory. I imagine it would have mentioned the word. If it did, the analysis would have been much the same as in my first post. I also fail to see what the issue is in accepting the validity of some US legal positions on imminence for the sake of the argument, and then showing that those arguments would most likely not succeed on the facts.

I must say that I find it strange to be accused of pro-American bias by people hiding behind pseudonyms (something we generally do not permit as a matter of editorial policy), when I argued that both the US and Iran military actions were illegal, the latter more straightforwardly so. If you have any specific argument as to why my analysis is mistaken, and in particular as to why the Iranian missile strike was lawful, then please do make it.

Veronika Bilkova says

January 9, 2020

Dear Marko,
thank you very much for your two interesting posts. I must admit that although I am not "yet another anonymous humble visitor" (well, I would like to keep "humble"), I am also a bit struck by the differences between the two posts.
The first one is very nuanced, scrutinizing various justifications the US has put or might put forward and then concluding that the attack on Soleimani was not clearly unlawful. In this post, conversely, you suggest there is only one legal theory that Iran could reasonably rely on (which, surprisingly, is somewhat different from the theory Iran actually relied on) and you conclude that it is "crystal clear that the strike was unlawful".
What is it exactly that makes you treat the two cases, which in your own assessment are very much alike, so differently?
You stress that the attack on Soleimani was over. Based on this argument, you reject classical self-defense and you only discuss pre-emptive self-defense / reprisals, merging somehow the two to conclude that the strikes were unlawful because the legal ground for retaliatory attacks simply does not exist under current international law.
First, classical self-defense – the ground on which Iran itself relied – could probably be discarded but I am not sure it is possible to do so based on “manifest unfoundedness” and without discussing the various factors that need to be taken into account (in the same way you did it for the US attack). Yes, the attack against Soleimani was over. But does the term “armed attack” in Article 51 of the UN Charter refer to specific incidents (attack on one person) or to the military action of one State against another more broadly? Could Iran have had reasonable grounds to believe there was such a military action against it going on? What about the theory of the accumulation of hostile actions which make up an armed attack? I am not saying these arguments are necessarily plausible either generally or in the case at hand. I am saying that the rejection of the classical defense justification would be more convincing for me, if based on the discussion of these arguments rather than on “manifest unfoundedness”.
Secondly, as to pre-emptive self-defense and reprisals. Here, I am a bit confused, because you do not seem to keep these two titles separate. You reject pre-emptive self-defense because: a) relying on such a theory would implicitly validate the US position and, b) the Charter does not permit any use of force, which is purely retaliatory in nature.
Ada) Well, it would validate the US theoretical position – PESD is a legal institution; it would not necessarily validate the relevance of this ground for the Soleimani case.
Adb) You say in your post on the US that the actions should be judged against the justification provided by the state itself. Here, however, you discard the official justification put forward by Iran (classical self-defence) and you focus instead on a justification which you deduce from political (!) statements (reprisals).
The combination of a+b makes you avoid a more thorough debate on pre-emptive self-defence (you engaged in such a debate, in a model way, in your post on the US). Provided that the US has not been less vocal about its plans to “take additional actions in the region as necessary to continue to protect US personnel and interests” and that Iran, in light of the Soleimani’s attack, might have some grounds to assume these actions could be directed against it, I think the pre-emptive self-defence justification (leaving aside its contested legality and the fact that Iran did not rely on this ground as explicitly as the US did) would warrant more attention. Thus, again, while not necessarily disagreeing with your conclusions, I am not wholly persuaded by the way through which these conclusions have been reached (or presented).
Finally, I am also confused by the IHL part of your post. If you see the events which have recently taken place in the region (the attack on Soleimani, the Iranian attack, etc.) as strictly isolated events which happen at one moment/place and are immediately over, I do not see how it would be possible to argue that an armed conflict between the two states exists (beyond those specific moments).

Marko Milanovic says

January 9, 2020

Dear Veronika,

I honestly think you are misunderstanding my position. I did not impute to Iran any justification that it did not itself offer. That justification is self-defence. The problem with Iran's view is, as I explained, that the attack which it was responding to was over. Iran could have said that it was trying to stop an ongoing series of attacks - but it never said that. It could have said that it was trying to prevent future imminent attacks - but it never said that. On the contrary, it did say that it targeted two bases from which the Soleimani strike was executed, which precisely indicated a punitive motive, as do the various statements by Iranian officials.

And after launching its missile barrage - which accomplished exactly nothing (thankfully so when it comes to the loss of human life), except sending a symbolic message - Iran said it concluded its defensive action. The nature of Iran's response directly undermines any theory that it was responding to an ongoing series of attacks or to an imminent attack. Its Article 51 letter to the UNSC expressly refers only to the cowardly attack against Martyr Soleimani and no other attack.

And in fact in the Oil Platforms case before the ICJ Iran expressly took the position that no anticipatory self-defence was permissible: So relying on an anticipatory theory would, in fact, have both accepted part of the US legal position and would have departed from a previous Iranian position.

I am not confusing self-defence and armed reprisals. What Iran did was use force. The issue is how that force is to be qualified. If the force was not used for the purpose of repelling an attack (ongoing or imminent), but was punitive in nature, it is properly qualified as an armed reprisal.

As for IHL, the issue of when and how IACs end is a complicated one. The basic rule is that they do so at the general close of military operations, which requires an ex post facto assessment of a degree of permanence and stability. Thus, while IACs start easily, they don't end as quickly. For an extensive discussion see the new ICRC commentary and also here:

So, again, I stand by my view that the Iranian strike was an illegal armed reprisal, clearly and unambiguously so. I am not hesitant to label US uses of military force as clearly unlawful, when they warrant that label - see e.g. here and

If you have a different view, that's obviously your prerogative.

Yet another humble visitor says

January 9, 2020

I would like to make clear that I wrote my comment in haste and that it has no bearing on my opinion that your posts are excellent.

I just have the impression (not only in this case), that too generous benefit of doubt is given to the US (and Western states in general), even in the academic circles.

P.S.: As far as I know, Iran also invoked self-defence (art. 51 of the Charter).

Kishor Dere says

January 11, 2020

It seems that states find it too difficult to comply with international law. Violating the law and justifying it on the grounds of national interest, sovereignty and even world peace appears to be much easier alternative than complying with it.

Anne Lagerwall says

January 24, 2020

Dear Marko Milanovic,

Thank you for your post who made me think deeply about the nature of the Iranian attack. I am a little doubtful that you can understand it as a punitive action. And I would be happy to have your views on the two following questions. First, couldn't one say that, in the light of the US sending additional troops in the region on 3 January, of speeches envisaging further attacks, of discourses making it clear that the US would not leave Iraq even after the Iraqi Parliament passed the bill asking for the withdrawal on 5 January, that all these events show that the drone strike was not an isolated and exceptional event, but prompted or was part of a broader agressive stance by the United States with respect to Iran ? Maybe, depending on information which may not be public, the armed attack started on 3 January but could be thought on 8 January to include other acts ? In that case, the armed attack would still be ongoing and the responsive attack would still be necessary ? Secondly, no State to my knowledge has explicitly affirmed that Iran could not be in self-defense against the United States (legally, they have criticized the fact that the Iranian attack occurred on Iraqi soil). How do you interpret what seems to be a certain acceptance of the claim made by Iran ?

If you are interested, Olivier Corten, Vaios Koutroulis, François Dubuisson and myself (all from the Université libre de Bruxelles) have published an analysis of diverse questions arising from the January crisis with regard to jus contra bellum, jus in bello and human rights. Pdf available here :