US and Israeli strikes against Iran, which have sparked a regional war, likely violate the UN Charter’s prohibition on aggression and lack any valid legal justification, experts say.

“This is not lawful self-defence against an armed attack by Iran, and the UN Security Council has not authorised it,” the United Nations special rapporteur on the promotion of human rights and “counterterrorism”, Ben Saul, told Al Jazeera.

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“Preventive disarmament, counterterrorism and regime change constitute the international crime of aggression. All responsible governments should condemn this lawlessness from two countries who excel in shredding the international legal order.”

The administration of United States President Donald Trump did not seek authorisation from the UN Security Council – or even from domestic lawmakers in Congress – for the war.

And Iran did not attack the US or Israel prior to the strikes that killed Iranian Supreme Leader Ali Khamenei and several other senior officials, as well as hundreds of civilians.

Yusra Suedi, assistant professor in International law at the University of Manchester, said there are grounds to believe that the attacks against Iran amount to a crime of aggression.

“This was an act of use of force that was unjustified,” Suedi told Al Jazeera.

International law is a set of treaties, conventions and universally accepted rules that govern relations between countries.

Imminent threat?

The Trump administration has argued that Iran posed a threat to the US with its missile programme and nuclear programme, arguing that military action was necessary.

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But the UN Charter prohibits unprovoked attacks against other countries.

“All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations,” the founding document of the UN says.

Rebecca Ingber, a professor at Cardozo School of Law at Yeshiva University who previously served as an adviser to the US Department of State, said that the prohibition of the use of force is a “bedrock” principle of international law that allows for only limited exceptions.

“States may not use force against the territorial integrity of other states except in two narrow circumstances — when authorised by the UN Security Council or in self-defence against an armed attack,” said Ingber.

Suedi said one instance in which the use of force can be legal is when a country seeks to thwart an imminent attack by another state.

Trump has said that the goal of the war is to “defend the American people by eliminating imminent threats from the Iranian regime”.

But Suedi cast doubt over that assertion.

“Imminence in international law is really understood to be something that is instant, something that is overwhelming, something that leaves really no other choice but to act first, something that is pretty much happening now,” Suedi said.

She noted that Trump himself had said repeatedly that the June 2025 US attacks on Iran “obliterated” the country’s nuclear programme, and that Tehran and Washington were holding talks when the war broke out on Saturday.

“There really was no evidence of an imminent threat, and that the attack was a pre-emptive strike,” Suedi told Al Jazeera.

“If it’s pre-emptive, it means that you are acting to counter something that is in the future, hypothetical, speculative, and that is not imminent, but that’s exactly what happened here. That is illegal under international law.”

US officials, including Trump, have said that Iran was building a ballistic missile arsenal to protect its nuclear programme and later build a nuclear bomb.

‘Scattershot’ arguments

Trump has also said that he is seeking “freedom” for the Iranian people, as the US president’s aides have described the regime in Tehran as brutal.

In January, Iran responded to a wave of anti-government protests with a heavy security crackdown. The violence killed thousands of people.

Trump encouraged the demonstrators to take over government buildings at that time, promising them that “help is on the way”.

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Experts say a humanitarian intervention to help protesters in Iran would have required UN Security Council authorisation to cross the legal threshold.

“The rationales have been scattershot,” Brian Finucane, a senior adviser for the US programme at the International Crisis Group, said of the US justifications for the strikes.

“Certainly none of them amount to a serious international legal argument.”

Beyond the possible breaches of the UN Charter, the US-Israeli attacks risk violating provisions of international humanitarian law that are meant to shield civilians from war.

An Israeli or US attack on a girls’ school in the southern Iranian city of Minab on Saturday killed at least 165 people, local officials have said.

“Civilians are already paying the price for this military escalation,” Annie Shiel, US Director at Center for Civilians in Conflict (CIVIC), told Al Jazeera in an email.

“We are seeing deeply alarming reports of attacks on schools and critical civilian infrastructure in Iran and across the region, with devastating casualties, including many children. These strikes risk igniting a wider regional catastrophe.”

Embrace of military power

The strikes on Iran are the latest instance yet of Trump’s reliance on the brute force of the US military power to promote his global agenda.

During Trump’s second term, the US has threatened to use military force to seize the Danish territory of Greenland, killed at least 150 people in a campaign targeting alleged drug trafficking vessels in Latin America, and abducted Venezuelan President Nicolas Maduro in a military attack that killed at least 80 people.

The legality of all of these policies has been questioned domestically and internationally, with UN experts saying that the boat strikes amount to extrajudicial killings.

Trump told The New York Times in January that he is driven by his own morality.

“I don’t need international law. I’m not looking to hurt people,” the US president said at that time.

In recent years, both Democratic and Republican US administrations have also continued to send Israel billions of dollars of weapons despite the Israeli military’s genocidal war on Gaza, which has been documented by rights groups and UN experts.

Ingber, the law professor, said that the use of wanton military force has contributed to a sense of impunity for powerful states and has degraded the international law system that has sought to place some constraints on conflict since the end of World War II.

“The prohibition on the use of force is a relatively recent innovation in the span of things. This rule is policed through the actions and reactions of states, and it feels fragile right now,” she said. “Do we want to go back to a world where states could use force as a tool of policy?”

Iran itself has lashed out against countries across the region in response to the US strikes, launching missiles and drones at military bases as well as civilian targets – including airports, hotels and energy installations.

“In the context of war, from the moment that the first strike was launched, the rules of warfare apply, and they’re very clear that civilian objects and spaces cannot be targeted,” Suedi said.

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She said Iran also appears to have violated international law with its response.

Suedi told Al Jazeera that Russia’s invasion of Ukraine and Israel’s brutal assault on Gaza have been showing the “unravelling fragility” of international law.

The war on Iran “is a next episode in that very worrying trend”, she said.