The UN nuclear watchdog criticized Iran on Wednesday for making an undeclared change to two clusters of advanced machines enriching uranium to up to 60% purity.

The International Atomic Energy Agency found that the interconnection between the two clusters of centrifuges changed during an unannounced inspection on January 21 at the Fordow Fuel enrichment Plant (FFEP), a site dug into a mountain where inspectors are stepping up checks after Iran said it would dramatically expand enrichment.

Fordow is so sensitive that the 2015 nuclear deal (JCPOA) between Iran and major powers banned enrichment there. Since the United States pulled out of the deal in 2018 and re-imposed sanctions against Iran, the Islamic Republic has breached many of the deal's restrictions on its nuclear activities.

In a confidential report to member states seen by Reuters, the IAEA did not say how the interconnection between the two cascades of IR-6 centrifuges had been changed except that "they were interconnected in a way that was substantially different from the mode of operation declared by Iran (to the IAEA)".

In a public statement summarizing that confidential report, the IAEA said its chief Rafael Grossi "is concerned that Iran implemented a substantial change in the design information of FFEP in relation to the production of high-enriched uranium without informing the Agency in advance."

"This is inconsistent with Iran's obligations under its Safeguards Agreement and undermines the Agency’s ability to adjust the safeguards approach for FFEP and implement effective safeguards measures at this facility."

The IAEA has had regular access to Fordow to carry out verification activities like inspections and it is in talks with Iran on stepping up those activities, the report said.

"The Agency and Iran have continued their discussions. The Agency has increased the frequency and intensity of its verification activities at FFEP. However, some other safeguards measures are still required and are being discussed with Iran," the report added.

Report by Reuters