Iran, for its part, insisted that it was cooperating fully with the International Atomic Energy Agency (IAEA) and any talk of possible further UN sanctions would be counterproductive.

The IAEA was "unable to provide credible assurance about the absence of undeclared nuclear material and activities," agency chief Mohamed ElBaradei told the body's 35-member board at the start of its regular year-end meeting.

"This is especially crucial in the case of Iran, because of its history of undeclared activities, and the corresponding need to restore confidence in the peaceful nature of Iran's nuclear programme," ElBaradei said.

Nevertheless, the IAEA "has no concrete information about possible undeclared nuclear material or weaponization activities in Iran", ElBaradei insisted.

And he urged Tehran "to be more pro-active in providing information... in order for the IAEA to be able to clarify all major remaining issues by the end of the year."

The Iran nuclear dossier was the dominant topic at the IAEA board meeting which diplomatic sources suggested could be wrapped up as early as Thursday evening.

And the focus was ElBaradei's latest report on Iran, in which the IAEA chief had declared the jury still out on the nature of Iran's nuclear activities, despite coming clean on a number of key past questions.

Crucially, Iran was continuing to defy repeated UN demands that it suspend uranium enrichment, a key phase in the nuclear fuel cycle.

Indeed, the fact that it is continuing to expand such activities had only reinforced the west's belief that Tehran is seeking to develop the nuclear bomb, despite's Iran's protestations to the contrary.

The IAEA "has so far not been able to verify some important aspects of Iran's nuclear programme: those relevant to the scope and nature of Iran's centrifuge enrichment activities, as well as those relevant to alleged studies and other activities that could have military applications," ElBaradei said in his opening address.

Over the two months, the agency had seen "an increased level of cooperation on the part of Iran," he noted.

Nevertheless, "the agency's knowledge about specific aspects of Iran's current programme has diminished since 2006, when Iran ceased to provide the agency with information under the additional protocol and additional transparency measures," ElBaradei said.

Iran's UN envoy Ali-Asghar Soltanieh insisted that Tehran had provided "all the information" the IAEA had requested and also allowed access to all the necessary sites.

"We have provided all the information and the agency has been visiting all workshops producing centrifuge machines, every piece of it," Soltanieh told reporters, referring to the centrifuges that are used to enrich uranium, a potential pathway to developing the atom bomb.

"We'll continue this mood of cooperation," the Iranian ambassador said, but warned that the "constructive approach" would be jeopardised by possible UN sanctions.

"Language of threat has always been counterproductive," Soltanieh warned.

If there was "peaceful dialogue and negotiation, then we show utmost flexibility as we have done" so far.

"But if you're going to use the language of threat or sanction, that will be counterproductive and it will definitely not work," Soltanieh said.

In Tehran, Iran's top nuclear negotiator, Saeed Jalili, said that a meeting with EU foreign policy chief Javier Solana would take place in London on November 30.

Solana must also report to the UN Security Council by the end of November before any decision is reached on possible further sanctions.

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