"This time the European side was more serious. That's why we consider the negotiations process more positive," Hossein Moussavian told state television.

"Both sides have begun practical talks, but there are still considerable differences between what we are demanding and the European position," he added.

"The Iranian delegation made it known to the Europeans that if the talks proceed with the same seriousness, cooperation is likely to continue beyond the initial three months," he said.

Britain, France and Germany are trying to convince Iran to dismantle an enrichment program the United States says is part of a covert atomic weapons development, in return for economic and political rewards.

Moussavian told state radio that the most taxing part of the talks was the guarantees demanded by the EU powers that Iran will not manipulate its fuel cycle in order to develop nuclear weapons.

"The most difficult part of the nuclear negotiations is the objective guarantees to ensure that Iran's fuel cycle does not deviate towards making an atomic bomb," Mousavian told state radio.

"There is a possibility that Iran reach an agreement with the Europeans, though the opposite could also happen," he added.

Tehran insists its talks with the European Union, represented by Britain, France and Germany, and which began in mid-December, must have concrete results within three months if they are to continue.

Iran's top nuclear negotiator, Hassan Rowhani, warned that if no deal was reached and the case referred to the UN Security Council, as demanded by the United States, Tehran could not bank on avoiding sanctions, newspapers said.

"If Iran does not reach an agreement with the Europeans on the nuclear issue, Iran's case will be referred to the Security Council, where it is unlikely one of the permanent members would use their veto in favor of Iran," he was quoted as saying.

Britain, China, France, Russia and the United States are permanent members of the UN Security Council.

Iran has formed important economic and political relations with Moscow and Beijing, with the Russians developing a nuclear plant in southern Iran.

On Friday, diplomats said EU negotiators had offered to send a mission to help Iran obtain a nuclear light-water research reactor, in what would be the first concrete move towards rewarding Tehran for abandoning uranium enrichment.

Iran insists that its nuclear program is purely civilian, but Washington, which states otherwise, is warily watching the EU-Iran talks set to continue next month.

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