When United States and Israeli forces struck Iran in February 2026, the world witnessed another open rupture of the international legal order that had already been straining under years of selective application. What has followed — the killing of Iran’s Supreme Leader, the restriction of the Strait of Hormuz, several ceasefire proposals, and deadly strikes across the region — has raised at least three overlapping questions that deserve serious answers: Was this lawful? How has the world responded? And does international law still mean anything when the most powerful actors simply ignore it?

The legal case against the strikes 

The US-Israeli strikes on Iran had no valid legal justification. Under Article 51 of the United Nations Charter, a state may use force against another only with Security Council authorisation or in genuine self-defence against an armed attack. In this instance, neither condition was met.

Israel asserted its inherent right to self-defence and the US claimed it acted pre-emptively against an imminent threat. But the threat it described — Iran’s potential nuclear capability and its general hostility — had existed, by Washington’s own account, for nearly five decades. Nothing can be imminent for forty-seven years. More awkwardly still, the US  subsequently contradicted its own justification, as its own intelligence indicated that no such attack by Iran was forthcoming (as stated by Iran on several occasions), and US President Donald Trump had separately declared that Iran’s nuclear programme had already been ‘obliterated’ by strikes in June 2025. 

President Trump also gestured toward a humanitarian rationale, urging Iranians to “take over” their government once strikes were complete. But humanitarian intervention — unilaterally attacking a state to protect its own population from its own government — is not an accepted basis for the use of force in international law.

Iran’s retaliatory strikes, meanwhile, created their own legal problems. Hitting US military bases across the Gulf was arguably lawful as self-defence — but Iran did not stop there. Civilian infrastructure in neighbouring states, including a hotel in Dubai, an airport in Kuwait, and residential buildings in Bahrain, was struck. This also took its response well beyond lawful self-defence, effectively making Iran the aggressor against the Gulf states themselves. Those states condemned the strikes, holding their own right to respond proportionately.

How the world Has responded

The response of the international community has been, at best, fractured — and at worst, a study in strategic, moral and diplomatic ambiguity. Among European states, Italy, Switzerland, Belgium, Norway, and Spain explicitly condemned the strikes as illegal — a notable cluster of dissent from close US allies. But a clear stance for or against the strikes was the exception, not the rule. Germany backed the strikes rhetorically while quietly withdrawing its own troops from the region. France criticised them publicly while simultaneously deploying anti-missile systems to Cyprus. Canada offered support ‘with regret.’ The United Kingdom stayed out of direct military involvement but permitted the US to use its bases in Cyprus and Diego Garcia — the latter a territory the International Court of Justice has already opined belongs to Mauritius, and which remains in legal limbo under an unfinished handover agreement.

When Trump called on allies to help keep the Strait of Hormuz open, he was largely rebuffed. Political and economic reasons certainly underpinned their position, but the legal reason is also instructive: collective self-defence — the only lawful basis for third-party military involvement — requires that the country invoking it was not the one that initiated hostilities. Since Iran’s actions in the Strait were a direct response to US and Israeli strikes, Washington’s ability to claim victim status was structurally compromised. Joining a coalition against Iran risked implicating those countries in the original aggression.

Yet the Strait of Hormuz remains a focal pressure point of this war. And beyond geopolitical struggles and economic dangers, Iran’s restriction of the Strait – through which roughly a fifth of the world’s oil passes – has produced its own legal tangle. Iran’s position rests on a deliberate substitution: the Strait is geographically a transit passage strait, connecting two open seas with no alternative route, which under the law of the sea gives other states an almost unrestricted right of passage that Iran can barely qualify. Iran argues instead that the Strait is an innocent passage strait: typically, a dead-end strait or one with an alternative route. Accordingly, the older rules of innocent passage apply — rules that give coastal states significantly more control — and that, unlike transit passage rules, those older rules have become sufficiently universal to bind Iran despite its non-membership of the UN Convention on the Law of the Sea (UNCLOS). Following this logic, it has allowed certain states to pass while restricting others aligned with the US or Israel.

The US, equally a non-party, counters that transit passage rules have themselves achieved universal status. That argument is genuinely contested, which is precisely the point: Iran has manufactured just enough legal ambiguity to sustain its position. The US has threatened it to open the Strait, while other states have opted for soft diplomacy, negotiating with Iran to let their ships through (some met with success). While the global economy risks paralysis, all eyes are on the Strait and states’ positions in this war therefore matter more than ever.

The conduct of war and the question of accountability

The question of whether to go to war is separate in law from the question of how war is fought. On the latter, the picture is bleak for all parties.

The US killing of Iran’s Supreme Leader Ali Khamenei — while he was a legitimate military target as Commander-in-Chief — was carried out in a manner that reportedly damaged a girls’ school. Israel struck large fuel storage tanks in Tehran, causing immediate shortages and toxic “black rain” — oil-saturated rainfall that poisons water supplies and damages crops. The US bombed Kharg Island, Iran’s primary oil export terminal, which handles the vast majority of Iranian crude oil exports. President Trump also threatened to obliterate Iranian power plants entirely. Iran targeted civilian infrastructure across the region in return. The International Committee of the Red Cross is unambiguous: energy infrastructure is civilian infrastructure. It may only be targeted if it qualifies as a military objective, and even then, the anticipated civilian harm — fuel scarcity, hospital outages, loss of heating — must not be disproportionate to the military advantage gained. Economic or political benefits do not count toward that calculation.

Israel also used white phosphorus in residential areas of southern Lebanon — a weapon that burns through skin and bone and cannot be extinguished. Iran deployed cluster munitions against Israel. Schools, hospitals, hotels, and historical landmarks have been struck by multiple parties.

The three core rules of warfare — distinction between civilians and combatants, precaution in attack, and proportionality in harm — bind all parties equally. They bind the aggressor and the defender alike. And crucially, they bind everyone regardless of whether a given treaty has been signed: these rules are now so universally accepted that they apply as a matter of customary international law. The fact that none of the main parties — the United States, Israel, Iran, or Lebanon — are members of the International Criminal Court (ICC) creates a challenge to accountability that could be displaced to domestic courts: some countries permit their domestic courts to try serious international crimes regardless of where they occurred. A US, Israeli, or Iranian military commander could, in principle, face arrest the moment they land in the wrong jurisdiction. 

What this moment reveals

This conflict has not produced a legal vacuum. The rules exist. The violations are identifiable. The question is whether any mechanism exists to enforce them against powerful states that choose to disregard them — and the honest answer, at this moment, is that the mechanisms are strained to their limits.

The United Nations Security Council is structurally incapable of acting when one of its permanent members is a party to the conflict or has a political interest in it. The ICC lacks jurisdiction over the key actors. European states are performing a delicate balancing act between legal principle and political alliance. The Global South is watching and drawing its own conclusions about which rules apply to whom.

What lies ahead? Could a ceasefire be on the horizon? The US has handed Iran a fifteen-point ceasefire proposal. Iran rejected it and offered a counterproposal. Whether the parties are negotiating remains unclear at the time of writing. 

But the legal problems embedded in the US proposal reveal at least two important observations about the structural obstacles to any durable agreement.

First, a bilateral US-Iran deal cannot legally bind the shipping nations, neighbouring countries, and proxy groups whose conduct will ultimately determine whether any agreement holds in practice. Obama’s 2015 Iran deal (the JCPOA) worked partly because it involved all five permanent Security Council members and the European Union. A two-party deal has neither that legitimacy nor that reach. 

Second, any agreement signed while Iran is still being bombed risks being voided under Article 52 of the Vienna Convention on the Law of Treaties, which invalidates deals concluded under the coercion of military force. Iran knows this, and it gives Tehran a ready legal exit from any commitment it later wishes to abandon.

If this conflict has demonstrated anything, it is not that international law is dead — it is that it is indispensable. Every violation has been accompanied by a legal justification, however strained. Every violation creates a greater desire for negotiation that returns, however reluctantly, to the same foundational rules. Every ceasefire proposal is an attempt to come back to the law and produce law for peace. The worst moments in international affairs have a way of reminding us why those foundations were laid in the first place.

Yusra Suedi is an Assistant Professor of International Law at the University of Manchester. She regularly writes on her blog, SAIL (Simplified Approach to International Law), that unpacks the international law driving today’s global headlines in plain language.