Iran and the Western parties to its 2015 nuclear deal have once more clashed over the country’s nuclear programme, this time after a report by the International Atomic Energy Agency (IAEA) on the sensitive Fordow uranium enrichment site.

The global nuclear watchdog said in a confidential report on Wednesday leaked by Western media that the interconnection between two cascades of advanced IR-6 centrifuges at Fordow had been changed in a way that was “substantially different” from what Iran had declared.

The agency also pointed out this is inconsistent with Iran’s obligations under a safeguards agreement required by the Treaty on the Non-Proliferation of Nuclear Weapons (NPT).

Iran’s nuclear chief, Mohammad Eslami, dismissed the report on Thursday by calling it “incorrect” and claiming an agency inspector had made a mistake.

“We immediately offered explanations that were communicated the same day and the agency inspector also became aware of their mistake,” he said, denouncing the fact that confidential IAEA reports are regularly leaked to the media.

But the E3 – France, Germany and the United Kingdom – and the United States, Western signatories to Iran’s 2015 nuclear accord with world powers that also included China, Russia and the EU, rejected Iran’s stance in a statement on Friday.

“We judge Iran’s actions based on the impartial and objective reports of the IAEA, not Iran’s purported intent,” they said, calling on Iran to fully cooperate with the agency.

“We recall that the production of high-enriched uranium by Iran at the Fordow Enrichment Plant carries significant proliferation-related risks and is without any credible civilian justification.”

The site at Fordow, which is dug into the mountains to protect it from potential attacks, in November saw a boost in the enrichment of uranium to 60 percent in reaction to a resolution passed at the IAEA board of governors that chided Iran for insufficient cooperation with the agency.

Iran had also turned off the remaining agency inspection cameras covered by the nuclear deal in June after another IAEA board resolution while maintaining that its nuclear programme is strictly peaceful.

The Fordow site is so important that enrichment there had been forbidden under the Joint Comprehensive Plan of Action (JCPOA), as the nuclear accord is officially known. But Iran has gradually abandoned any limits set in the accord after the US unilaterally withdrew from it in 2018 and imposed sanctions.

Talks to restore the deal remain deadlocked since September, with the US publicly maintaining it does not currently prioritise advancing the talks following deadly protests in Iran, while Tehran claims Washington is secretly sending messages to reach an agreement.

The latest clash on Fordow comes as IAEA Director General Rafael Grossi had said last month he hopes to visit Tehran in February to hold talks with Iranian officials on the unresolved cases of nuclear particles found years ago at several Iranian sites.