The United Nations nuclear watchdog reported on Wednesday that Iran has begun generating enriched uranium using more efficient advanced centrifuges at its Fordow site, which is excavated into a mountain, further undermining the 2015 Iran nuclear agreement during discussions with the West to save it.

The move looked to undercut indirect discussions between Iran and the US to pull both parties fully back into the tattered accord, which restarted this week following a five-month hiatus caused by the election of hardline President Ebrahim Raisi.

Western negotiators are concerned that Iran is fabricating facts on the ground in order to gain influence in the talks.

The International Atomic Energy Agency (IAEA) announced on the third day of this round of negotiations that Iran has begun the process of enriching uranium to up to 20% purity using one cascade, or cluster, of 166 modern IR-6 machines at Fordow. These machines are significantly more efficient than the IR-1 of the first generation.

That arrangement does not enable Iran to enrich uranium at Fordow at all, emphasizing how severely the deal has deteriorated. Iran had previously produced enriched uranium using IR-1 machines and had enriched with certain IR-6s without storing the product.

The IAEA claimed in a statement that it has 94 IR-6 machines placed in a cascade at Fordow that is not yet operational.

A more comprehensive IAEA report circulated to member states and seen by Reuters said that as a result of Iran’s move the nuclear watchdog planned to step up inspections at the Fordow Fuel Enrichment Plant (FFEP) that houses the centrifuges, but the details still need to be ironed out.

Iran played down the report as routine despite the fact that the IAEA, which does not explicitly give a reason for such reports, typically issues them only for significant developments such as fresh breaches of the deal’s nuclear restrictions.

“The recent report of the IAEA on Iran’s nuclear activities, is an ordinary update in line with regular verification in Iran,” Iran’s permanent mission to the U.N. organizations in Vienna said on Twitter.

However, IAEA Director General Rafael Grossi made clear he viewed the development with concern.

“This redoubles the alert. It is not banal. Iran can do it, but if you have such an ambition you need to accept inspections. It’s necessary,” Grossi told French broadcaster France 24.

Iran and major powers are trying to revive the 2015 deal under which Tehran limited its nuclear programme in exchange for relief from U.S., EU and U.N. economic sanctions.

U.S. then-President Donald Trump abandoned the deal in 2018 and reimposed harsh U.S. sanctions, angering Iran and dismaying the other parties: Britain, China, France, Germany and Russia.

This week’s indirect talks between Tehran and Washington – with others shuttling between them because Iran refuses to meet U.S. officials – have made no visible progress.

Iran’s foreign ministry spokesperson on Wednesday accused Israel of “trumpeting lies to poison” the talks.

While it was unclear what the spokesperson was referring to, a Tel Aviv-based reporter for U.S. news organization Axios on Monday reported that Israel had shared intelligence with Washington and European allies suggesting Iran was taking technical steps to prepare to enrich uranium to 90% purity, the level needed for a nuclear weapon.

Iran says its nuclear programme is for purely peaceful purposes.