Nuclear talks between Iran and world powers came to a standstill Tuesday as Tehran said it did not want France to be part of any deal on uranium enrichment.

Iran's delegation left the headquarters of the International Atomic Energy Agency in Vienna late in the day without ever sitting down for a second day of talks with US, French, Russian and IAEA officials.

Iran's IAEA ambassador Ali Asghar Soltanieh did not indicate where he was going or whether he would return with his team later Tuesday, but diplomats insisted that their departure did not amount to a walkout.

"No-one has walked out of the talks," one diplomat told AFP.

The diplomats participating in the closed-door meeting, which began Monday, also said there was no link between the delay and 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 a proposal has been made 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.

"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."

The IAEA also did not say why the second day of talks had been delayed, even though all the delegations had gathered at the UN watchdog's headquarters.

On the first day of the talks Monday, IAEA chief Mohamed ElBaradei had said the negotiations had gotten off to a "constructive" start.

But delegates briefly assembled in the room on Tuesday morning before deciding to delay the start.

The teams from Tehran and Paris appeared to make a point of leaving the room together.

Paris, too, insisted the delay was not over Mottaki's comments.

"It is a meeting of experts, in which we are participating," French foreign ministry spokesman Bernard Valero said.

"The discussions are continuing. There are many technical parameters to take into account for the supply of nuclear fuel and we will see later which states will take part," Valero said.

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 an informed 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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