The motion brought by the United States, Britain, France and Germany -- but voted against by China and Russia -- is the second of its kind within six months and comes amid an impasse over undeclared uranium particles found in Iran.

This is the second critical resolution this year, after one in June, on the subject of a lack of "technically credible" answers provided by Iran regarding the particles.

In the absence of progress in recent months, Washington, London, Paris and Berlin have decided to increase the pressure.

The resolution underscores that it is "essential and urgent" for Iran to "act to fulfil its legal obligations".

The IAEA has been pressing Iran to provide answers on the presence of undeclared uranium of man-made origin found at three sites in the past, including "access to locations and material", as well as the collection of samples.

The resolution was carried by 26 votes in favour versus two against, with five abstentions and two countries absent, diplomats told AFP.

- Iran denounces pressure -

Before the vote on the resolution, the US delegation to the UN in Vienna said in their national statement to the board that "Iran must now provide the necessary cooperation, no more empty promises".

The EU delegation expressed their serious concern over the lack of progress from Iran in clarifying and resolving the outstanding safeguards issues.

Iran had denounced the resolution yesterday, stating that "documents which... are not true" were put forward.

Russia's ambassador to the UN in Vienna Mikhail Ulyanov echoed that position after the resolution was passed on Thursday.

"From the Russian viewpoint, it is better than in June when a similar resolution got 30 votes in favour," he tweeted.

The impasse over the agency's probe comes as wider talks to revive the 2015 nuclear deal are stalled.

The years-long probe has been a key sticking point that led to a similar resolution criticising Tehran in June.

At the time, the Islamic Republic responded to it by removing surveillance cameras and other equipment from its nuclear facilities.

The 2015 agreement Iran reached with Britain, China, France, Germany, Russia and the United States gave Tehran relief from sanctions in return for guarantees it could not develop an atomic weapon.

Iran has always denied wanting a nuclear arsenal.

The deal collapsed after Washington's unilateral withdrawal in 2018 under then president Donald Trump.