The meeting comes the day after US Secretary of State Condoleeza Rice warned that the European Union was not being tough enough with Iran.

But on Thursday Britain, France and Germany "are going to read the riot act to the Iranians," a diplomat close to the talks told AFP earlier in the week.

The nuclear issue is coming up in talks between officials in Geneva that opened Tuesday, marking the third round in negotiations that began in December after Iran agreed with the European trio to temporarily suspend uranium enrichment as a confidence-building measure.

Britain, France and Germany are pushing diplomacy as the trio leads an EU initiative to get Iran to widen the suspension into a permanent dismantling of its program to enrich uranium, a key part of the nuclear fuel cycle, in return for trade, technology and political security goodies.

While discussion of technology and trade cooperation and then political and security issues each took one day, the nuclear issue could take two days, a second diplomat said.

This shows European determination to get some sort of result on the core issue in the talks, as diplomats have said there will be no progress on delivering incentives until Iran agrees to abandon enrichment.

The stakes are even higher after Rice's comments, with the United States supporting the EU diplomacy but holding off from getting directly involved.

Washington charges that Iran is secretly developing nuclear weapons and wants to increase pressure by getting the UN watchdog International Atomic Energy Agency (IAEA) to bring Tehran before the UN Security Council, which could impose sanctions.

Rice said in a Fox television interview that "the Iranians need to hear that if they are unwilling to live with verification measures... then the Security Council referral looms."

"I don't know that anyone has said that as clearly as they should to the Iranians," said Rice, who was in Brussels Wednesday on a European tour.

But in an apparent attempt to soften her criticism of the Europeans, Rice later told a news conference: "I think a diplomatic solution is in our grasp if we have unity of message and unity of purpose."

US President George W. Bush said he was "very pleased" with European leaders' response to Rice's call for a harder line on Iran's nuclear program.

"The Iranians just need to know that the free world is working together to send a very clear message: Don't develop a nuclear weapon," Bush said in Washington.

The European trio is set to warn Iran about activities that verge on breaches of the deal to freeze uranium enrichment, the process which uses centrifuges to make nuclear fuel for reactors but which can also be the explosive core for nuclear bombs.

Britain, France and Germany are following advice from IAEA chief Mohamed ElBaradei "who has warned Iran in two letters in December and January" about quality control work on centrifuge parts despite the agreed halt to all enrichment-related work, the first diplomat said.

But Iran has warned that it is running out of patience.

Iranian President Mohammad Khatami said Wednesday that Tehran could reverse commitments made on its nuclear programme, saying Iran was faced with 'psychological warfare'.

Iran refuses to make its suspension permanent, saying it has the right to enrichment under the nuclear Non-Proliferation Treaty.

Iranian Foreign Minister Kamal Kharazi said in Japan Wednesday that Iran had no secrets to hide from the IAEA, which has been investigating Iran's nuclear program for two years.

"I assure Mr Minister that all our activities are peaceful," Kharazi told a joint news conference after talks with Japanese Foreign Minister Nobutaka Machimura.

"We are ready to cooperate with the IAEA as before and also to continue talks and negotiations with the three European countries," he said.

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