Top diplomat and nuclear negotiator Hossein Moussavian, quoted by the state news agency IRNA, complained that Britain, France and Germany had so far "not shown any seriousness".

Iran was "seriously doubting their capacity" to strike a deal, he said.

Top cleric and powerful former president Akbar Hashemi Rafsanjani also told a nuclear technology conference in Tehran that "three months have passed and we have seen nothing yet.

"If we feel that no progress is being made, there is no point losing time," he said of the talks with Britain, France and Germany. "We are waiting for them to make marked progress in the coming days."

Rafsanjani also told reporters that Iran viewed its suspension of uranium enrichment -- a process that could be diverted to building bombs -- was only a six-month halt and that the country still wanted to resume nuclear fuel work.

But the so-called EU-3 are trying to convince Iran to dismantle its fuel cycle -- seen by the United States as part of a covert atomic weapons development -- in return for economic and political rewards.

The Europeans see a halt as the only way Iran can provide "objective guarantees" it will not use its atomic energy drive for military purposes.

But Iran insists its nuclear programme is purely for civilian energy needs, and that its fuel cycle work is therefore permitted by the nuclear Non-Proliferation Treaty (NPT).

A fourth round of talks starts in Geneva on Wednesday and Thursday.

"We have said clearly to the Europeans that a halt (of enrichment) is not acceptable," said another Iranian negotiator, Cyrus Nasseri.

He also asserted that Iran was instead thinking of building "10 other Natanzes" -- a reference to the enrichment facility in the centre of the country.

And foreign ministry spokesman Hamid Reza Asefi told reporters that any demand for Iran to completely halt its enrichment activities went beyond the deal reached in Paris last October that kicked off the current round of talks.

"The text of the Paris agreement was in English. There was nothing about permanent suspension. It mentioned 'objective guarantees', which means we continue enrichment and they are assured that no deviation is done," he said.

"We want to make it clear we are not haggling. We are not looking for incentives."

The spokesman also asserted that the Islamic republic was not concerned about US threats of being hauled before the UN Security Council.

"We do not want to have our case referred to the UN Security Council. It could be solved by the IAEA (International Atomic Energy Agency) and the EU. But, if it is referred, we are not worried," Asefi said.

"If the Americans, the Europeans or anyone else think they can threaten Iran with the Security Council so Iran will give up its legitimate right, they are mistaken and one day they will regret it. This is Iran's red line."

But despite the defiant tone, prominent analysts said Iran may yet accept a deal with the EU but is likely to delay any decision until after crucial presidential elections in June.

"I think those negotiations are in limbo right now. I do not think any progress has been made because Iran has not decided yet whether it is prepared to accept limits on its enrichment programme," explained Gary Samore, Director of Studies at London's International Institute for Strategic Studies.

"In the run-up to the presidential elections, I do not think any of the Iranian officials have any interest in showing any flexibility because they will be strongly criticised for giving away Iran's rights," he explained.

"So I think we have a period of time now when people are exploring different ideas. But I do not think political decisions have been made in Tehran about whether or not to really seek a diplomatic solution."

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