UN nuclear chief Yukiya Amano urged Iran Monday to start answering questions about alleged nuclear weapons projects and accused Tehran's leaders of evading the issue through round after round of negotiations.

"To be frank, for some time now we have been going around in circles," the director general of the International Atomic Energy Agency (IAEA) said at a regular meeting of the agency's governing board in Vienna.

Senior IAEA officials held a 10th round of inconclusive negotiations with Iranian counterparts in Vienna in May, in an effort finally to gain access to suspect sites, officials and documents that could shed light on the weapons allegations.

Amano stressed again that the Parchin military site was of key interest to the IAEA, where key nuclear weapons components were allegedly tested around the year 2003.

Western diplomats said last week they would hold off censuring Iran at this board meeting, but that they might take such a step in September, one year after the board told Iran to allow IAEA investigations immediately.

Amano reported in May that Iran has also been pushing ahead with its controversial uranium enrichment and with building a plutonium-producing reactor at Arak, against the demands of the UN Security Council.

"This report is a clear indication that Iran is successfully continuing its nuclear activities for peaceful purposes," Iran's IAEA envoy Ali Asghar Soltanieh told reporters Monday.

He was referring to the fact that the IAEA inspectors have not found any evidence that Iran is trying to use its enrichment plants or Arak to make weapons fuel, despite Western fears that the facilities might one day be used for such a purpose.