Are the US–Israeli strikes on Iran justified under international law?

The US-Israeli air and missile strikes across Iran on Saturday have raised renewed questions about the two nations’ alleged breaches of international legal norms.  

Legal experts have repeatedly denounced US and Israeli attacks over the past year, including those of last June, as illegal under international law. 

For Marko Milanovic, a professor of public international law at the University of Reading School of Law, who has written extensively on the topic, that argument still stands. 

“The strikes are clearly illegal, in that they are a breach of the UN Charter, which prohibits unilateral resort to force between states,” he told Middle East Eye after Saturday’s strikes.

“Self-defence is the only possible exception to that prohibition that Israel and the US could rely on, but the requirements for lawful self-defence are not met.”

Later on Saturday, Iran launched retaliatory strikes on Israel as well as various Gulf states.

Explosions were heard in Saudi Arabia, the UAE, Kuwait, Bahrain and Qatar, where US bases have been targeted.

It is unclear how many Iranians have been killed so far. However, a strike on a school in southern Iran has killed more than 150 girls, believed to be aged between seven and 12.

How do the US and Israel justify the strikes?

US President Donald Trump said early on Saturday that the operation was aimed at preventing Tehran from obtaining a nuclear weapon and "eliminating imminent threats from the Iranian regime".

He also suggested that regime change is among the objectives of the attacks.

"When we are finished, take over your government," he said in comments intended for the opposition inside Iran. "It will be yours to take. This will be probably your only chance for generations.”

Israel's Prime Minister Benjamin Netanyahu said the attack "will create the conditions for the brave Iranian people to take their destiny into their own hands" and "remove the yoke of tyranny". Defence Minister Israel Katz described it as a pre-emptive strike against threats to Israel.

What does international law say about using force?

The UN Charter prohibits states from using force under Article 2(4),  except in two cases:

1. When authorised by the UN Security Council

2. In self-defence under Article 51, if an armed attack occurs against a UN member state

The Security Council did not authorise the 28 February strikes, leaving only the claim of self-defence for possible justification.

International law also criminalises the use of force unless in the circumstances above. Therefore, officials responsible for the attacks may be held accountable if found guilty before domestic or international tribunals.

Although no state leader has been prosecuted for this crime, aggression is one of the four core international crimes under the Rome Statute of the International Criminal Court (ICC), alongside genocide, crimes against humanity, and war crimes.

It refers to the planning, preparation, initiation or execution of an act of aggression, or the use of force in violation of the UN Charter, by a person in a leadership position, such as a head of state or senior military commander. However, the ICC’s jurisdiction for aggression would not extend to American, Israeli or Iranian leaders, since these states are not parties to the ICC's founding treaty.

Did Iran launch an attack justifying US/Israeli self-defence?

There was no Iranian armed attack on US or Israeli territory immediately before the strikes of 28 February.

Without such an attack, states must rely on anticipatory self-defence, which is, in the view of some states, lawful only when an attack is imminent, Milanovic explained. Other states, especially from the Global South, reject the view that self-defence is possible even against imminent attacks which are yet to occur.

Can self-defence apply if there is no armed attack?

International law distinguishes three views with respect to self-defence, according to Milanovic:

1. Preventive self-defence, used to counter long-term or hypothetical threats. This is widely rejected by virtually all states and legal experts because it would allow states to strike whenever they perceive a distant danger.

2. Anticipatory self-defence, permitted only when an attack is genuinely imminent, either in a strict temporal sense (about to happen) or in a broader causal sense (the attacker has the intent and capability to commit the attack, and now is the last window of opportunity to deflect that attack).  

3. Self-defence after an attack, which is the strict reading of Article 51

According to Milanovic, the first view is unlawful under the UN Charter. The third, strict view, would make the US-Israeli strikes manifestly illegal.

Even under the anticipatory approach, which falls between preventive and strict, the strikes appear unlawful because neither the intent nor the immediacy of an Iranian attack has been demonstrated.

What about claims that Iran posed an imminent nuclear threat?

The operation against Iran has been partly justified as a way to prevent Tehran from advancing towards a nuclear weapon.

But there's no evidence that Iran is seeking to develop a nuclear weapon, and Iranian leaders have repeatedly denied the allegations, saying their nuclear programme is for civilian purposes only. 

Neither US intelligence nor the UN nuclear watchdog has found any evidence that Iran was pursuing an atomic weapon, a narrative Israel and some in the Trump administration have nevertheless pushed.

Trump himself in June declared Iran's nuclear facilities had been "obliterated" in US strikes that month. 

Oman's foreign minister, the main mediator in the US-Iran talks, said on Friday, hours before the US-Israeli attack, that Iran had formally agreed to "never, ever have nuclear material that will create a bomb”. 

“Iran does not yet have a nuclear weapon, nor is there any proof that its leadership would use that weapon against the two states,” said Milanovic.

Under international law, imminence requires clear evidence that the attacking state intends to strike; and a narrow time window in which the defending state must act to avoid being hit.

“Some states argue that self-defence is also possible against imminent armed attacks. But even on the broadest possible understanding of imminence, there was no such attack by Iran against the US or Israel,” Milanovic added.

Was the operation necessary and proportionate?

Even if a state could claim anticipatory self-defence, the use of force must still be necessary and proportionate. Strikes must be the last resort to stop an imminent attack.

According to Milanovic, “attacking Iran while negotiations are ongoing is hardly a defensive act that was strictly necessary”.

The scale of the operation also raises questions about proportionality, but it’s difficult to assess this on its first day.

Does Iran have the right to respond militarily?

Iran is entitled to self-defence under international law, says Milanovic. 

“Iran has the right to defend itself, so long as it acts in a way that is necessary and proportionate,” he told MEE. 

“Again, it’s a bit too early to say whether its armed response has remained within these bounds. It is, however, problematic for Iran to attack facilities in third states, such as Saudi Arabia, which have not been used to commit the attack against it.”