Iran is determined to resume some of its sensitive nuclear activities in defiance of a deal with the European Union, Tehran's top nuclear negotiator said earlier in the day.

The country's nuclear programme is the focus of international fears that the clerical regime is seeking to develop nuclear weapons. Iran insists it only wants to make atomic energy reactor fuel.

"Let's wait and see what actually happens," Blair said at a press conference when quizzed about a response to Iran's threats.

"But we certainly will support referral to the UN Security Council if Iran breaches its undertakings and obligations.

"Quite how that will come about we have got to work out with our colleagues and allies.

"But those international rules are there for a reason, and they have to be adhered to."

Foreign Secretary Jack Straw, who has been closely involved in negotiations with Iran alongside France and Germany, warned Tehran that it stood to lose various favours pledged by the United States, including support for an application to join the World Trade Organisation.

"Those unquestionably will be lost because they were part of the negotiations taking part in the context in which Iran had agreed ... to maintain its suspension of uranium-enrichment and related activity," Straw told BBC radio.

He said London wanted Tehran to be able to run its nuclear energy power programme but not produce material that could be used for weapons.

"There is no conclusive evidence that is what they are up to," said Straw.

"They say they are not. The problem is that what is incontrovertible is that there is a 20-year history of them failing to disclose aspects of their activities."

Straw warned, however, that the resumption of uranium-enrichment activities would prompt Britain to seek to convene an emergency meeting of the board of the International Atomic Energy Agency (IAEA) "and/or we could end up in the Security Council.

"We don't want to do either of those, but it was Iran who decided to go down this track."

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