US Secretary of State Mike Pompeo travels to the UN Thursday to activate a controversial mechanism aimed at reimposing international sanctions on Iran, in a disputed move that threatens the Iranian nuclear deal.

Pompeo will tell the Security Council president, currently Indonesia, at a 2:00 pm (1600 GMT) meeting that the US is triggering the so-called "snapback" procedure, which its European allies are set to contest.

The move widens the gulf between the US and the other permanent members of the Security Council on Iran policy that 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.

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, 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 reinstall 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 where the United States acts as if the sanctions have been reimposed and the rest of the Council continues as before.

Pompeo will also discuss the move with United Nations Secretary-General Antonio Guterres at Guterres' residence in New York during a meeting at 2:30 pm.

America's top diplomat is then due to brief press at the UN at 3:30 pm.