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:
Iran took & concluded proportionate measures in self-defense under Article 51 of UN Charter targeting base from which cowardly armed attack against our citizens & senior officials were launched.
We do not seek escalation or war, but will defend ourselves against any aggression.
— Javad Zarif (@JZarif) January 8, 2020
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.