The head of the United Nations' nuclear watchdog, the International Atomic Energy Agency (IAEA), has demanded that Iran provide all details of its nuclear activities.
Tehran denies it has a nuclear weapons programme
IAEA chief Mohammed ElBaradei said Iran has been showing
increased co-operation, but that his experts still do not
have enough information to determine the nature of Tehran's
"I would urge Iran in the coming weeks...to demonstrate full
transparency by providing the agency with a complete and
accurate declaration of all its nuclear activities," Mr ElBaradei said.
He was speaking as the IAEA began a week-long series of meetings focussing on concerns about Iran's nuclear programme.
A closed-door session of the IAEA's governing board is examining a report by its inspectors, which says traces of weapons-grade uranium were found at an Iranian nuclear plant.
Iran denies its uranium enrichment activities are part of an illegal weapons programme.
It says it is seeking to produce only low-grade uranium fuel to meet its energy needs.
"It's part of our job over the coming weeks and month is to determine the veracity of this statement," IAEA Chief Spokesperson Mark Gwozdecky told BBC News Online.
The United States accuses Iran of trying to develop nuclear weapons and wants the UN agency to condemn it for violating the nuclear non-proliferation treaty
BBC regional analyst Sadeq Saba says Iranian leaders must be pleased - at least for the time being- that they have escaped with Mr ElBaradei's mild criticism.
If Iran had been found in non-compliance of its nuclear obligations, as the Americans had apparently hoped, the matter would have been taken up by the UN Security Council, which could impose sanctions.
ElBaradei has visited Iran twice this year to investigate the issue
However, our correspondent adds, the dispute over Iran's nuclear ambitions is not over yet and the international community is watching Tehran carefully.
Mr ElBaradei urged the Iranians to sign up to an additional protocol that would allow intrusive snap inspections of its nuclear facilities.
The Iranian delegate at the agency, Ali Akbar Salehi, said if things went well at the board meeting, his country would soon take a decision on such a protocol.
Mr ElBaradei has been to Iran twice this year, while his inspectors have made frequent visits.
The widely leaked report says that in August, Iran belatedly admitted that it had carried out uranium conversion experiments in the early 1990s which should have been declared.
Iran has shown increased co-operation over the past three months, both in terms of providing information on its nuclear activities and allowing the inspectors access to nuclear sites, the report notes.
But it also points out that some of the information was in contrast to that provided earlier.
The report insists that Tehran needs urgently to clarify certain key questions, not least about the traces of weapons-grade uranium found by agency inspectors at the enrichment plant at Natanz.
But it stops well short of finding Iran in non-compliance with its obligations under the non-proliferation treaty.
For its part, Iran insists its nuclear activities are peaceful, devoted solely to generating electricity, and has warned that too much pressure from the US and its allies could be counterproductive, aggravating tensions rather than easing concerns.