The Vienna-based International Atomic Energy Agency (IAEA) said on Sunday it had been denied "indispensable" access to the TESA Karaj centrifuge component manufacturing workshop near Tehran contrary to a September 12 agreement with Iran.

Iran's ambassador to the IAEA Kazem Gharibabadi on Monday rejected the charge on Twitter.

"During the discussions in Tehran and Vienna, Iran indicated that... equipment related to this Complex are not included for servicing," he wrote, referring to IAEA work on its surveillance equipment.

Sunday's IAEA statement "isn't accurate and goes beyond the agreed terms," he added.

At a Vienna meeting of the IAEA board of governors, the EU said it urged Iran to allow access "without any further delay", expressing its "deepest concern".

"This is a worrying development," the statement said.

This month's agreement between the IAEA and Iran came days after the nuclear watchdog had decried a lack of cooperation from Tehran.

Agency inspectors had been allowed to service monitoring and surveillance equipment and to replace storage media at "all necessary locations" except the TESA Karaj workshop, the IAEA said on Sunday.

IAEA Director General Rafael Grossi in his latest report on Iran informed member states that the Islamic republic had granted all other access from September 20-22.

The IAEA's latest report comes amid stalled EU-brokered negotiations to revive a 2015 landmark agreement scaling back Iran's nuclear programme in exchange for sanctions relief.

That deal started to fall apart in 2018 when the US withdrew from it and reinstated sanctions. Iran in turn again started to ramp up its nuclear activities.

Talks began in April in Vienna between Tehran and the remaining five parties to the 2015 deal aimed at bringing Washington back into the agreement.

But that dialogue has been stalled since June, when ultraconservative Ebrahim Raisi won Iran's presidential election.

Iran's foreign minister said Friday that talks would restart "very soon", but the US has called for a clear timetable.

"(It's) important #ViennaTalks resume asap from where we left off on 20 June," Vienna-based EU Ambassdor Stephan Klement wrote on Twitter on Monday.