Are the US attacks on Iranian nuclear facilities lawful?

Limits on the use of force

According to the UN Charter, the use of force by states is only permitted under very strict conditions: in cases of self-defence or with the approval of the UN Security Council. Arcuri identifies this as one of the cornerstones of international law. "One of the fundamental norms of international law is the prohibition on the use of force, which, after the end of World War II, has been codified in Article 2(4) of the UN Charter and is reflected in customary international law," Arcuri explains. She continues: "Article 2(4) reads: 'All Members shall refrain in their international relations from the threat or use of force …'." Given that the UN Charter's core value is maintaining peace, the lawful use of force remains limited to these very exceptional circumstances. 

The controversy over pre-emptive strikes 

Article 51 of the UN Charter clarifies that an attack must have occurred before a state can lawfully invoke the right to self-defence. Arcuri elaborates on a recent case: "The easiest case is when a state has been attacked by another, as in the case of Ukraine in 2022. In this case, Ukraine could lawfully invoke its right of self-defence against Russia. Also, the acts of self-defence, to be lawful, should be necessary and proportional. Things get more complicated when an attack has not occurred (yet)." 

The United States sought to justify its airstrikes as collective self-defence in support of its ally Israel. In doing so, it relied on an even more contested legal basis: pre-emptive self-defence. Arcuri explains: "In simple words, this doctrine means that you have the right to defend yourself before an attack starts. This doctrine has been rarely invoked in practice, but it has been defended by some scholars and a few states, such as Israel and the US. Many other scholars and states reject the legality of pre-emptive self-defence because such a doctrine is out of line with the wording of the Charter and could lead to abuse, as it would depend on a unilateral and partial assessment of the threat and likelihood of an attack." Arcuri is also highly critical: "Accepting this doctrine uncritically risks stretching self-defence to a point where anything can justify intervention, hollowing out the very core of the prohibition of the use of force as any state could at one point wage war against a hypothetical attack from a non-friendly country. For these reasons, it is widely accepted that, if self-defense is to be invoked lawfully, an attack should at least be ‘imminent.’ And there was no imminent attack by Iran.”  

'Last resort' as legal justification 

At the heart of the debate around pre-emptive strikes lies this requirement of 'imminence'. Arcuri clarifies: "The concept of 'imminence' is to be understood temporally. Few scholars and states have tried to stretch this concept beyond its temporal dimension, articulating the test of 'a last window of opportunity' that would allow attacking preventively, even when the attack is only expected in the future. This doctrine has been explicitly rejected by an overwhelming majority of countries; hence, it cannot be considered part of customary international law." 

She quotes another lawyer who has studied this matter who stated: " the 'last window of opportunity' test is not the law. And that is a good thing, too. In the best-case scenario, widespread adoption of the test will lead to states making potentially catastrophic errors concerning whether other states actually intended to attack them." 

The case of Israel and the United States: A breach of the UN Charter? 

Since the United States presented its actions as collective self-defence and as assistance to Israel, the legality of its airstrikes depends, according to Arcuri, on whether Israel's own attacks on Iran were lawful. Arcuri is clear: both the Israeli and American attacks are unlawful. "Israel considers its attacks as pre-emptive self-defence in relation to the threat posed by the development of nuclear weapons by Iran. Such justification is not legally tenable because there is no evidence that Iran would have built a nuclear bomb in the immediate, let alone that it would have been able and willing to use it against Israel. If Israel's actions do not qualify as lawful self-defence, then neither do the US military's bombings of Iranian facilities." 

Some academics argue that there is an ongoing armed conflict between Israel and Iran. Even then, Arcuri says, the attacks would not be lawful: "Even if one would accept the framing of the 'ongoing conflict', which is highly controversial among scholars, the requirements of proportionality that would apply in such a case would likely be missing.  The bombing of Iranian nuclear facilities, the targeted killing of the several leaders of the Iranian regime, the targeted killing of scientists and the killing of almost 400 civilians are not proportional." According to Arcuri, the US attacks may go beyond violations of the UN Charter: "The deliberate targeting of scientists by the Israeli military are likely violations, also of international humanitarian law if they were not members of the Iranian armed forces." 

Retaliation also has limits 

In response to the attacks, Iran launched rockets at Israel. Whether this was lawful depends on the proportionality and targeting of the retaliatory actions. Arcuri: "Only those actions that aimed at repealing the Israeli armed attack can be justified as self-defence. While some response from Iran could be considered self-defence, Iran has also to respect international humanitarian law. The missiles hitting the Hospital in the Israeli town of Beersheba could also be a violation of international humanitarian law." 

In this way, Arcuri emphasises that international law not only sets limits on the initiation of force, but also on the response to it. Retaliation is not a license. Every party in a conflict must act within the boundaries of international law. 

What if Iran were to build nuclear weapons? 

Arcuri also briefly addresses the hypothetical scenario in which Iran actually develops nuclear weapons. In response to whether an attack would be lawful in such a case, she states: "The possibility that Iran might develop nuclear weapons does not justify the attacks.  To be clear, Iran did and does not have the bomb. According to the New York Times, US intelligence agencies assessed that Iran did not yet decide to pursue the construction of a nuclear weapon, even though it accumulated a significant stockpile of enriched uranium capable of supporting such an effort. Even if a nuclear weapon could have been assembled within months - as it has been claimed - this did not indicate that Iran had either the capability or the intent to use it." 

Disturbing trends 

Finally, Arcuri reflects on the broader implications of this kind of violence for international law: "Violations of (international) law do not per se erode the law. Violations have always been there in international law (and in domestic legal systems). What is most worrying, in my view, are two trends. One is to dismiss international law as irrelevant. We hear analysts talking increasingly of geopolitics, as if the law does not matter. This type of performative speech (regrettably more normalised in hegemonic countries, like the US) is very dangerous, as it may contribute to weakening the international law system." 

The second worrying trend, she says, is the adoption of double standards: "European countries have vehemently condemned the Russian invasion of Ukraine. They have been much more timid in condemning the widespread war crimes committed in Gaza and the clear violations of international law by Israel and the US in the June attacks on Iran." 

Law is the protection of the individual 

Arcuri concludes with a powerful message about international law's moral and human value: "Given the interconnectedness of life on Earth, it is today more important than ever to uphold international law. International law, as imperfect as it may be, is the legal system that could help states, International Organisations and other relevant actors to cooperate on the global plane. Here I have to think of the words of Hersh Lauterpacht, the lawyer behind the ideation of crimes against humanity during the Nuremberg trials: 'the individual human being … is the ultimate unit of all law.'" 

She closes with a deeply personal reflection: "Then, I have to think of the child passionate about Judo, a Yoga teacher, a 24-year-old poetess who participated in the Tehran protests since 2022 and was still walking in the streets of this town, inhabited by 10 million people, without a veil. They, who live no longer, remain for me the ultimate unit of international law and of its violations."