Iran said on Saturday it was close to an agreement with France, Britain and Germany that would enable it to resume sensitive nuclear activities that have been frozen for months.
The three European Union powers persuaded Iran to suspend activities related to uranium enrichment late last year to reassure the world it was not seeking nuclear arms, as Washington alleges. Iran said this week it would soon resume such activities.
The three EU foreign ministers sent a letter on Wednesday to Iran's chief nuclear negotiator Hassan Rohani warning him that breaking the suspension now would end talks and that they would then back US moves to refer Iran to the UN Security Council for possible sanctions.
But Mr Sirus Naseri, a senior Iranian negotiator in the EU talks and Iran's chief delegate to the U.N. nuclear watchdog, said Tehran was not far from a deal with the Europeans that would allow it to resume work at a uranium processing plant.
"We are not at all far from having a working agreement on the resumption of Isfahan, as long as there is a firm intention (to reach an agreement) there on the side of the Europeans," Mr Naseri told Reuters after a series of meetings in Vienna with UN and European officials.
EU negotiators -- who said at the beginning of the month they were far from a deal and that the talks were about to collapse -- were not immediately available for comment.
The facility at Isfahan converts raw "yellowcake" uranium into processed uranium gas. This gas can then be fed into centrifuges that spin at supersonic speeds to refine it for use as fuel in nuclear power plants or weapons.
Backed by Washington, the EU has demanded that Iran make the suspension permanent in exchange for economic and political incentives. But Iran insists it has a sovereign right to a uranium fuel programme which it will never abandon.