Tensions between Iran and the International Atomic Energy Agency (IAEA) have repeatedly flared since a 2015 deal curbing Tehran's nuclear programme in exchange for sanction relief fell apart.

Iran has increased its stockpile of enriched uranium in recent months, reaching more than 32 times the limit set in the 2015 accord with world powers. The stockpile was estimated at 6,604.4 kilogrammes as of October 26, up 852.6 kilos from the last quarterly report in August.

The confidential report follows a visit last week by IAEA head Rafael Grossi to Tehran for talks with President Masoud Pezeshkian and other top officials.

During the visit, "the possibility of Iran not further expanding its stockpile of uranium enriched up to 60 percent was discussed," the report said.

"On 16 November 2024, the agency verified... that Iran had begun implementation of preparatory measures aimed at stopping the increase of its stockpile of uranum enriched up to 60 percent," it added.

According to the IAEA, Tehran is the only non-nuclear weapon state to enrich uranium to 60 percent, a short step from the 90 percent level needed for atomic weapons.

Iran has always denied seeking a nuclear weapon.

"Exchanges between the agency and Iran on this matter are expected to continue," the report said.

The report comes on the eve of the IAEA board of governors meeting, where European powers -- backed by the United States -- seek to censure Iran for its poor cooperation with the UN nuclear watchdog.

Diplomats told AFP that the planned censure is driven by a need to raise diplomatic pressure on Iran to come back into compliance and address the IAEA's long-standing concerns.