Top nuclear negotiator Cyrus Nasseri told AFP that "the Russians have made a proposal" under which Iran would apparently be able to resume uranium conversion work at a plant in Isfahan, but the gas produced would be sent to Russia for the ultra-sensitive process of enrichment.

The resulting nuclear fuel would then be transferred back to Iran to power the Bushehr power station, which is being built with Russian assistance.

"We are in the process of examining this proposal," Nasseri said, but gave no further details.

However his comments were at odds with Washington, who said a similar proposal had been made by Iran -- and not the Russians.

"There is apparently an Iranian idea like this that they have floated with the Russians," State Department spokesman Richard Boucher said Friday, before going on to rubbish the proposal.

"Let me point out a couple of things: First of all, Russia has already agreed to provide at least the first decade's worth of enriched uranium fuel for Iran's nuclear reactor at Bushehr," he said. "So Iran would have no need to do any conversion work whatsoever."

The proposal, which the US says is Iranian, "only reinforces our view that Iran's enrichment and conversion effort is, in fact, designed to contribute to the capabilities that are needed to develop nuclear weapons."

Boucher said the US, Russia, the EU and the International Atomic Energy Agency (IAEA) "have all agreed that Iran should not be allowed to develop the capabilities necessary to make nuclear weapons."

Iran agreed in November with Britain, France and Germany to suspend its uranium conversion and enrichment activities, which Washington believes conceals its nuclear armament intentions.

However the Islamic republic is seeking to resume uranium conversion, a move that would violate its deal with the EU-3 and leave it facing the threat of UN Security Council action.

Emergency talks between Iranian nuclear negotiator Hassan Rowhani and the three European foreign ministers are due to take place on Tuesday and Wednesday.

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