Tensions between Iran and the UN nuclear watchdog have repeatedly flared since a 2015 deal curbing Tehran's nuclear programme in exchange for sanctions relief fell apart.

The IAEA said in its quarterly report that it is of "serious concern" that Iran has an estimated amount of 274.8 kilograms enriched to up to 60 percent as of 8 February, up by 92.5 kilograms since the last report in November.

It comes after Tehran in December announced plans to ramp up production of highly enriched uranium to 60 percent, which is a short step from the 90 percent level needed for atomic weapons.

According to the IAEA, Tehran is the only non-nuclear weapon state to enrich uranium to 60 percent.

Iran has always denied seeking a nuclear weapon.

"The significantly increased production and accumulation of high enriched uranium by Iran, the only non-nuclear weapon State to produce such nuclear material, is of serious concern," the report said.

It comes on the eve of the IAEA board of governors meeting.

Donald Trump unilaterally withdrew the United States from a landmark 2015 deal with Tehran during his first term as president. The deal had exchanged sanctions relief for limits on Iran's nuclear programme.