"Up until now and from the start of the process, especially since the Paris meeting (March 23), the Europeans have not undertaken any serious step to bring it to a close," said Hossein Mussavian, spokesman for the negotiating team.

"If this tendency is confirmed and the Europeans do not change their attitude, I am very pessimistic," he told AFP ahead of Friday's next round of talks in London.

In The Hague, Iran's Foreign Minister Kamal Kharazi said he hoped the negotiations would be "successful and come up with tangible results".

Kharazi said if there was no agreement or the talks collapsed, "it is our right to restore the programme" of uranium enrichment which has currently been halted for the duration of the talks.

The process makes fuel for nuclear power reactors but also the explosive core of atom bombs.

Friday's talks are "crucial" to see if the Europeans are "serious", he added. "Iran is not interested in delaying tactics that will take a long time without results."

The European Union, represented by Germany, Britain and France, has been negotiating with Iran since December 2004 to get objective guarantees that Tehran would not use its nuclear program to build weapons.

Iran froze enrichment last November as a confidence-building measure to start the talks with the EU, which is offering trade, security and technology rewards if it makes the suspension permanent.

On Friday, Iran will meet again with the European trio to discuss the nuclear programme, which Washington suspects is being used as cover to build the bomb. Each new round of talks is generally preceded by Iranian warnings.

"If there is no result, Iran will consider changing its current policy," Mussavian said.

He ruled out any indefinite suspension of uranium enrichment. "Insisting on a halt would kill off the process," Mussavian warned. "Iran has never accepted nor will it accept a halt to enrichment."

According to diplomatic sources in Tehran, the Iranians are proposing to resume enrichment but on a limited scale.

Iran has proposed to resume the assembly, installation and experimental use of 3,000 centrifuges -- which are used for enrichment -- at its factory in Natanz, south of the capital.

But the Europeans are standing firm against the idea, they said.

Ali Agha-Mohammadi, a spokesman for Iran's Supreme National Security Council, which is in charge of the nuclear dossier, also warned that Tehran could review its participation in negotiations with the Europeans.

"The negotiations will go on if there is progress at (Friday's) meeting," Agha-Mohammadi said on state radio. "But if the Iranian delegation does not see any progress then the process will change radically," he said on state radio.

"(In that case) there is no question that we would reconsider the negotiations process because that would be a violation of the Paris accord," he said, referring to a deal in late 2004 that paved the way for the talks.

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