The UN nuclear watchdog on Wednesday "categorically" denied its cameras played a part in a June attack on an Iranian nuclear facility, after Tehran said it was investigating the possibility.

In a report seen by AFP, the International Atomic Energy Agency (IAEA) said its "Director General categorically rejects the idea that Agency cameras played a role in assisting any third party to launch an attack on the TESA Karaj complex."

Iran has told the IAEA that "its 'security and judicial authorities' were 'investigating whether the terrorists have used the Agency cameras to launch an attack on the complex'," the report said, referring to a building near the city of Karaj about 50 kilometres (30 miles) from the capital Tehran.

The latest report comes just days before talks are due to restart in Vienna on reviving the 2015 deal on Iran's nuclear programme.

IAEA Director General Rafael Grossi is also scheduled to visit Iran on Monday, according to Iran's atomic agency.

Iran has called the incident at Karaj a "sabotage" and has accused its arch-foe Israel of carrying out.

Also in the report on Wednesday, the IAEA said Iran had increased its stockpile of highly enriched uranium, defying commitments made under the 2015 nuclear deal.

Its estimate of Iran's stockpile, as of November 6, was 2,489.7 kilogrammes, many times in excess of the limit laid down in the 2015 agreement with world powers.

The total amount now includes 113.8 kg enriched to 20 percent, up from 84.3 in September, and 17.7 kg enriched up to 60 percent, up from 10 kg, the report said.