Iran returned to nuclear talks with world powers late Tuesday after furious diplomacy to salvage the negotiations on a uranium enrichment deal which had come to a standstill.

Iranian, US, Russian and French officials resumed their talks at the headquarters of the International Atomic Energy Agency in Vienna after the American and Iranian sides met separately under the auspices of the IAEA.

The talks, which started on Monday, had appeared on the verge of collapse earlier Tuesday when the Iranian delegation left the building without any explanation and after Tehran said it did not want Paris to be part of a deal.

But all sides eventually returned to the negotiating table for about an hour and IAEA chief ElBaradei, who attended the talks, said they would meet again on Wednesday.

The talks are over a proposal for Russia and France to enrich below-weapons grade uranium for Iran. Western powers want greater control of Iran's uranium which they fear is being used to build a nuclear bomb.

"We still hope to be able to reach an agreement. It's a complex process," ElBaradei told reporters.

"There are technical aspects, many technical issues that we have to hammer out. It is of course a question of confidence buiding, of guarantees," he said.

"I think and I believe that we are making progress. It is maybe slower than I expected but we are moving forward and we are going to meet tomorrow at 10:00 am."

Shortly before talks resumed, the US and Iranian sides met separately in ElBaradei's office "to move forward on the implementation of the agreement reached in principle" at a previous meeting this month in Geneva, said Michael Hammer, spokesman for the US National Security Council.

Diplomats participating in the closed-door meeting insisted that the long delay on Tuesday had nothing to with comments by Iranian Foreign Minister Manouchehr Mottaki that France was not needed at the talks.

"We have two separate issues: what Mottaki said in Tehran and the fact that there has been no formal meeting so far today. But the two aren't related," a diplomat told AFP on condition on anonymity.

Another diplomat said the delay "is not about the continued French participation but rather about how to best structure a deal so that everyone can be satisfied".

Iran has told the IAEA it needs fuel for a research reactor and it agreed in principle in Geneva to send uranium to be processed in France and Russia.

But Mottaki said France was not needed.

"The agency contacted some countries and the United States and Russia accepted to participate in the negotiations to supply the fuel," Mottaki said.

"The negotiations will be conducted with these two countries in the presence of the agency. We do not need a lot of fuel and we do not need the presence of many countries. There is no need for France to be present."

But Paris insisted it was still on board.

"Iran does want to speak with France," French Foreign Minister Bernard Kouchner said in Paris after the talks resumed.

On Monday, Iranian media said Tehran did not want France at the negotiating table because it had not fulfilled "previous obligations regarding nuclear cooperation with Iran."

State-owned Al-Alam television channel quoted a source close to Tehran's negotiating team in Vienna as saying France "does not have an acceptable record and since it also obstructed the negotiations between Iran and the IAEA."

Iran has 1,500 kilogrammes of low-enriched uranium at its plant in Natanz, in defiance of three rounds of UN sanctions to back demands that it halt all enrichment activity.

But it needs a higher level of enrichment to run a research reactor in Tehran, which makes isotopes needed for medical use such as cancer treatment.

Western powers suspect Iran has embarked on research to build a nuclear bomb. Iran has denied the claims but has been accused by the IAEA of not cooperating with efforts to determine whether its atomic programme is peaceful.

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