Jubilant scenes broke out this weekend in several European cities as members of the Iranian diaspora celebrated after US and Israeli strikes killed Iran’s Supreme Leader, Ayatollah Ali Khamenei. In Brussels, some revelers described the moment as historic, while elsewhere EU officials struck a more cautious tone, condemning Tehran’s conduct but stopping short of endorsing the attacks.
EU governments now confront a familiar, uncomfortable choice: how to respond to strikes that supporters describe as targeting a dangerous regime and critics say killed scores of civilians. The Iranian Red Crescent reports at least 555 civilian deaths in addition to Khamenei, a figure that has intensified demands for scrutiny over the strikes’ legality.
Washington framed the operation as part of a campaign to prevent Iran from acquiring nuclear weapons and to degrade its missile capabilities. President Donald Trump said the US was ensuring that “the world’s number one sponsor of terror could never obtain a nuclear weapon.” Defense Secretary Pete Hegseth dismissed international institutions as constraints, saying the US would act “regardless of what so‑called international institutions say,” and criticized allies who voiced concern.
Those positions are resonating unevenly across the EU. Germany’s Chancellor Friedrich Merz has been careful not to publicly rebuke Washington, arguing that legal nitpicking would do little to alter Iran’s behaviour and that this is not the moment to lecture allies. Spain’s Prime Minister Pedro Sánchez, by contrast, condemned the unilateral strikes as an escalation that makes the international order more unstable.
Legal experts remain split. Marc Weller, director of Chatham House’s international law programme and a professor at Cambridge, contends there is no available legal justification for a sustained attack on Iran. He says international law allows force only in response to an armed attack or as a last resort when no other means can avert one, and that humanitarian intervention thresholds were unlikely met by Iran’s internal repression.
Rosa Freedman, professor of law, conflict and global development at the University of Reading, argues legal texts must be interpreted in context. She points to decades of Iranian threats in the region and explicit nuclear ambitions, and says that when read with the UN’s purpose in mind, the strikes aimed at preventing a nuclear capability can be seen as lawful.
Practically, the legal debate is unlikely to be resolved in court. The UN Security Council could take measures, but any attempt to sanction the US or Israel risks a veto from Washington or its allies, limiting the council’s ability to enforce a unified legal judgment. As Freedman put it, more powerful states have greater capacity to act as they choose.
Weller warns of wider consequences if unlawful uses of force are tolerated. Normalising such action, he says, could erode the principled framework that underpins Europe’s ability to criticize others, making it harder to oppose future aggression by states like Russia or deter expansionist moves by China without facing charges of double standards.
The UN Security Council met to discuss the crisis, but deep divisions among major powers make a single, cohesive response unlikely. The unresolved debate over legality, precedent and principle now sits at the center of a broader concern: whether a fragmented European response will weaken the EU’s credibility and its diplomatic leverage on the world stage.
Reporting from Brussels contributed to this piece by Xenia Polska and Finlay Duncan. Edited by Carla Bleiker.