The military attack launched by the United States and Israel against Iran is illegal under American law and international law? Many have raised this question, given the manner in which the governments of Washington and Tel Aviv suddenly decided to bomb the Islamic Republic.

Trump reportedly sent a "notice" to Congress but did not seek authorisation for the attack

Let us start with United States legislation: the war began without any parliamentary vote — let alone approval. Congress was not formally involved in the decision, even though President Donald Trump had long made clear that the military option could certainly not be ruled out.

For this reason, although many Republican members of Congress welcomed news of the strikes, numerous Democratic lawmakers branded the armed action "illegal". "The president has plunged our country into a war against Iran without seeking any authorisation from Congress," thundered Senator Jack Reed. "Trump never made his case, never tried to persuade parliament. He does not even have a plan for how the war itself ends."

Numerous US lawmakers: "Attack on Iran is illegal"

"The military attack is illegal and unconstitutional. These are unlawful acts that fuel the risk of escalation, posing serious threats to American troops and civilians in the region," echoed Senator Ed Markey. House Democratic Minority Leader Hakeem Jeffries agreed, according to CBS News.

Under the Constitution of the United States, Congress is in fact the sole body empowered to declare war. "In the absence of exceptional circumstances, authorisation is required," Markey noted. And the very nature of the "pre-emptive operation" emphasised by the White House underscores that no such exceptionality existed in the case of Iran, since no immediate threat was identifiable.

Elizabeth Warren ✓ @SenWarren

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Trump's war against Iran is illegal and a betrayal of the American people.

Congress cannot allow Trump to drag yet another generation into a forever war.

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A position shared by Senator Elizabeth Warren, as well as by a leading figure of the British left, Jeremy Corbyn.

Jeremy Corbyn ✓ @jeremycorbyn

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Allowing British bases to be used in an illegal war of aggression is a catastrophic and historic mistake.

Britain has been dragged into another war because our Prime Minister would rather appease Donald Trump than stand up for international law.

War is not a game. This

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The US–Iran negotiations that had reached a positive "breakthrough" in Geneva come to nothing

All the more so given that, for days, negotiations between representatives of Tehran and Washington had been under way in Geneva, mediated by Oman. According to Oman's Foreign Minister, on the very Friday in question — just hours before the attack — a "breakthrough" had been reached, as the Islamic Republic had for the first time agreed to stop stockpiling enriched uranium. Not only was a dialogue open, but it was also bearing fruit.

For her part, White House Press Secretary Karoline Leavitt defended the decision by stating that Marco Rubio had provided Congress with "a notice". There is, however, a clear difference between a briefing and a request for authorisation.

The United Nations Charter prohibits the use of armed force except in "self-defence" in the event of "aggression"

From the standpoint of international law, moreover, the rules that must be observed are clear. The United Nations Charter has prohibited the use of armed force in relations between states since 1945, except in self-defence in the event of aggression. The problem is that the legal definition of the word "aggression" has remained vague for decades, and to this day — as absurd as it may seem — there is no single, universally agreed definition of "armed conflict" (although numerous Conventions attempt to delineate its contours and parameters).

For a war to be fully "legal", it must also pass through approval by the UN Security Council. The definition enshrined in the UN Charter is, moreover, a product of its historical moment: the immediate post-Second World War period, during which there was near-unanimous determination to prevent a new tragedy like the one that had just ended. Yet since then, in the face of dozens upon dozens of wars that have broken out across the world, authorisation has been granted in only a very small number of cases, such as the wars in Korea in 1950, Kuwait in 1991 and Afghanistan in 2001.

Criticism of the United States and Israel from Norway, Spain and the United Nations

It is no coincidence that numerous governments have criticised the United States over the attack on Iran. According to Norwegian Foreign Minister Espen Barth Eide, the military action "does not comply" with international law. This is because "a pre-emptive attack presupposes the existence of an imminent threat". Similarly, Spanish Prime Minister Pedro Sánchez spoke of a "unilateral action by the United States and Israel", stressing that the Madrid government "demands immediate de-escalation and full respect for international law". Spain's Foreign Ministry likewise called for adherence to "the UN Charter and international humanitarian law".

United Nations Secretary-General António Guterres took the same line, calling on "all member states to respect their obligations". He recalled that the Charter "clearly prohibits" the use of force against the territorial integrity of any nation.

Donald Trump: "Limits to my powers? Only my own morality"

Beyond the obligations tied to international law, there is also the matter of relations with NATO allies, none of whom – according to a series of statements from heads of state and government – had been informed of the attack.

Peter Baker ✓ @peterbakernyt

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Asked if there any limits on his global powers, Trump tells @nytimes "Yeah, there is one thing. My own morality. My own mind. It's the only thing that can stop me." He adds, "I don't need international law." @SangerNYT @tylerpager @katierogers @KannoYoungs nytimes.com/2026/01/08/us/…

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It is hard to imagine, in any case, that the criticism raining down on the United States could lead the White House to change course: even in the case of the overthrow of Nicolás Maduro's regime in Venezuela, numerous diplomatic services had challenged the "method" employed by Washington. But in a recent interview with the New York Times, Trump answered in no uncertain terms when asked whether there are any limits to his powers of intervention in the world: "Yeah, there is one thing. My own morality. My own mind. It's the only thing that can stop me."

Iran, is the war illegal? What international law and the US Constitution say