"That's up to the Iranians who they send to sit across the table from the EU-3," State Department spokesman Sean McCormack told reporters.

Iran's state news agency IRNA, citing a well-informed source, reported that Supreme National Security Council head Hassan Rowhani, who had led the Islamic state's talks with the European Union over its nuclear program since October 2003, had "presented his resignation to President Mohammad Khatami".

However Ali Agha Mohammadi, spokesman for the council, immediately told AFP in Tehran that the announcement was "totally false".

The good-humoured personality of the white-bearded cleric Rowhani has become appreciated in European capitals during the precarious negotiations on the nuclear program.

"Rowhani's departure would be a very bad signal," said a top European diplomat close to the negotiations.

The uncertainty over Rowhani's future comes less than two weeks after the ultra-conservative Mahmood Ahmadinejad was elected Iran's president, thrashing rival candidate Akbar Hashemi Rafsanjani, a close ally of Rowhani and moderating influence on nuclear policy.

It also comes at a delicate phase in negotiations between Iran and the European Union that are aimed at persuading Tehran to give guarantees its nuclear programme is peaceful in exchange for a wide-ranging cooperation deal.

Rowhani has been in charge of the nuclear portfolio since October 2003 and has succeeded in keeping talks alive despite threats by the United States to take Iran to the UN Security Council.

Ahmadinejad's landslide victory has worried European countries, who fear Iran could one day decide to resume its sensitive uranium enrichment activities, frozen for the course of the negotiations.

The talks with Europe will be entering a critical phase, with Iran expecting concrete proposals on the nuclear cooperation deal from the so-called EU-3 comprising Britain, France and Germany by the end of this month.

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