"It is unlikely that we will resume enrichment, that is to say the activities at Natanz. But some activities at the UCF (Uranium Conversion Facility) at Isfahan could resume next week," top negotiator Hassan Rowhani was quoted as saying by the IRNA and Mehr news agencies.

Rowhani, the secretary of Iran's Supreme National Security Council, said "the current process cannot continue in the way the Europeans want it to and Iran could take new decisions." He added that "a definitive decision on whether or not to resume uranium enrichment will be taken next week" by the Islamic republic's leadership.

Uranium conversion involves turning raw uranium into UF6 gas. That can be fed into centrifuges that refine out enriched uranium, which can be directed towards making fuel for atomic reactors or the core of a nuclear weapon. Uranium conversion is covered by a freeze agreed to by Iran in November 2004 under a deal that kick-started a series of talks with Britain, France and Germany that are aimed at easing international fears the Islamic republic is seeking the bomb.

If Iran carries through its most serious challenge yet of the EU deal, it risks being hauled before the UN Security Council for possible sanctions. The EU, backed by the United States, wants Iran to halt all nuclear fuel cycle activities -- fearing enrichment technology would give Iran the capacity to produce a bomb. In return, it is offering a package of trade, security and technology incentives.

Iran unsatisfied with talks

But after the latest round of talks with the EU in London on Friday, top national security spokesman Ali Agha Mohammadi told AFP Iran was "unhappy."

"The negotiations were good on content and there were principled agreements, and the Europeans were closer than ever to our point of view," said Mohammadi, a spokesman for Iran's Supreme National Security Council. "But concerning the application and the timetable, Iran is unhappy with the results," he added.

Iran has said repeatedly that its enrichment suspension is temporary and voluntary, as it insists on its right under the nuclear Non-Proliferation Treaty to make nuclear fuel. Mohammadi said the Iranian side "feel the Europeans are merely trying to delay" a resumption of enrichment.

Also speaking in London after the talks, Iranian negotiator Cyrus Nasseri said "some progress" had been made but there was still no agreement. "We believe there has been some progress on the framework for a long-term agreement ... the difference is about the timing," Nasseri told AFP.

According to diplomatic sources, the Iranians are seeking agreement on the "assembly, installation and testing of 3,000 centrifuges in Natanz," the site where Iran wants to build an enrichment plant and has already set up a pilot project of 164 centrifuges.

A cascade of about 2,000 centrifuges could produce enough highly enriched uranium in a year to make one atom bomb, experts say, although Iran has said it would produce only low-enriched uranium. Iran wants to be able to expand the facility to eventually include more than 50,000 centrifuges, which would be an industrial level of production.

Next step open

Nasseri said: "We have examined further the elements of this phased approach which we believe covers the concerns and interests of both sides in an equitable manner. The difference however is about the timing, particularly of the initial stage. We have not been able to move forward on this and the situation is going to be evaluated in the capitals," he said, referring to London, Paris, Berlin and Tehran, which are now assessing the outcome of Friday's meeting.

Iran has been subject to more than two years of investigations by the International Atomic Energy Agency, which has discovered plenty of suspicious nuclear activity but no "smoking gun" that proves a weapons drive. The country insists it only wants to generate nuclear power in order to meet increased domestic energy demands and reduce its dependence on oil and gas -- a vital source of hard currency.