Secretary of State Mike Pompeo submitted a letter to the president of the UN Security Council notifying him of Iran's "significant" non-compliance with the terms of the 2015 historic accord, according to a copy seen by AFP.

The letter, delivered personally to Indonesia's UN ambassador -- who currently holds the Council's rotating presidency -- in New York triggered the beginning of a disputed procedure called a "snapback."

The move widens the gulf between the US and the other permanent members of the Security Council on Iran policy, which began when President Donald Trump withdrew from the nuclear accord with Tehran in 2018.

The procedure, never before used, comes after the US suffered a humiliating defeat at the Security Council last week when it failed to muster support for a resolution to extend a conventional arms embargo on Iran.

The snapback aims to restore all international sanctions against Iran that were lifted as part of the 2015 nuclear agreement with Tehran in exchange for it agreeing not to develop nuclear weapons.

But it also threatens to torpedo that historic deal, known officially as the Joint Comprehensive Plan of Action (JCPOA), which Britain, France and Germany -- along with Russia and China -- are trying to save.

A Security Council resolution ratifying the accord, which was negotiated by former president Barack Obama, says participating states can unilaterally reimpose sanctions if Iran has failed to significantly comply with the accord.

The snapback procedure is supposed to lead to the re-establishment of sanctions after 30 days, without the possibility of any members, namely Russia and China, wielding their vetoes.

European countries on the Security Council say the US gave up their right as a participant when Trump pulled out of the deal in May 2018 and reimposed American sanctions as part of his "maximum pressure" campaign against the Iranian regime.

Experts say the snapback threatens to plunge the Security Council into crisis and raise questions about the legitimacy of its resolutions.

They foresee a situation in which the United States acts as if the sanctions have been reimposed -- and the rest of the Council continues as before.

- 'Lasting damage' -

"There's no doubt the Trump White House is using snapback as a desperate last gambit to burn the JCPOA house down before the US elections," Ellie Geranmayeh, an Iran expert at the European Council on Foreign Relations, told AFP.

"This move will leave the UN Security Council in one big mess, with competing narratives among world powers over if the UN sanctions against Iran should be reinforced," she said.

"What it does do is leave a lasting damage for the UN Security Council and further isolates the US position on Iran."

Pompeo was also due to discuss the move with United Nations Secretary-General Antonio Guterres at Guterres' residence.

America's top diplomat was then due to brief media at the UN.