Vienna: UN nuclear watchdog chief Mohammad Al Baradei on Friday said his agency had made "quite good progress" in clarifying Iran's nuclear programme thanks to Iranian cooperation, but serious doubts persist.

The International Atomic Energy Agency (IAEA) head made the comments as the agency issued a new report on Iran's behaviour. "In the last four months, in particular, we have made quite good progress in clarifying outstanding issues," he said.

"On that score, Iran in the last few months has provided us with visits to many places that enable us to have a clearer picture of Iran's current programme. However, that is not, in my view, sufficient," he said.

While the report painted a more positive picture of Iranian cooperation than before, it also confirmed Iran was testing technology that could give it the means to enrich uranium much faster - in defiance of demands to halt all sensitive nuclear activity or be hit with wider UN sanctions.

The findings may be branded negative by big powers and spur the UN Security Council to adopt more sanctions as early as next week.

Iran has said it has satisfactorily answered all relevant IAEA questions about past activities, its nuclear slate is now clean and sanctions are unjustified and illegal.