The International Atomic Energy Agency (IAEA) has been pressing Iran to provide answers on the presence of undeclared nuclear material found at three sites.

The IAEA probe has been a key sticking point that led to a resolution criticising Tehran in June.

A delegation by the UN nuclear watchdog was due to visit Tehran by the end of this month, but Iran's atomic energy chief Mohamed Eslami reportedly said earlier Wednesday that no such visit was planned "for the moment".

"Maybe it is lost in translation... but we hope that this technical meeting" aimed at resolving outstanding issues will happen, Grossi told a news conference in Vienna.

"Some doubt" was now hanging over the visit by senior agency officials, Grossi said, but he added that he was hopeful Iran would be able to "clarify" that.

A quarterly report by the agency last week also concluded there had been "no progress" in the long-standing investigation.

Traces of undeclared uranium of man-made origin had been discovered at three Iranian sites in the past.

The issue has been a point of contention during on-off talks between Tehran and world powers to revive a 2015 landmark deal that sought to curb Iran's nuclear programme in exchange for sanctions relief.

"We have responded to all of the IAEA's allegations and accusations and, if it had good intentions and a will to continue negotiations, they (Western countries) would not have presented a resolution" against Iran, the official IRNA news agency quoted Eslami as saying.

- Iran rejects resolution -

Late Tuesday, diplomats said that a fresh resolution rebuking Iran had been submitted to the IAEA's board of governors.

Tehran immediately rejected the resolution put forward by Western nations calling on Iran to cooperate fully with the IAEA.

"They wrote a resolution and brought documents which they themselves know are not true and which are rejected by the Islamic republic," Eslami said.

The resolution will be discussed during a quarterly meeting of the IAEA's 35-nation board of governors that began on Wednesday.

The draft text seen by AFP underscored that it was "essential and urgent" for Iran to "act to fulfil its legal obligations".

It comes against the backdrop of stalled talks on reviving the 2015 nuclear deal.

The deal Iran reached with Britain, China, France, Germany, Russia and the United States gave it 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.