Iran threatened yesterday to halt snap UN inspections of its nuclear sites and resume uranium enrichment if it was reported to the UN Security Council as agreed by the council's five permanent members.

The big powers said a crisis meeting of the International Atomic Energy Agency (IAEA) board tomorrow should "report to the Security Council on the steps required from Iran".

But they said the council should then wait until IAEA chief Mohamed ElBaradei reports on Iran's nuclear programme at a regular IAEA meeting on March 6 before deciding on any action. That gives Tehran a few more weeks to try to negotiate its way out of the crisis, but its immediate response was defiant.

"We will never abandon our rights to nuclear technology and if referred to the Security Council, Iran will stop voluntary implementation of the Additional Protocol," Iranian President Mahmoud Ahmadinejad was quoted as saying by the semi-official Mehr news agency.

The nuclear Non-Proliferation Treaty's Additional Protocol, signed but not ratified by Iran, gives UN inspectors greater powers of access to suspected sites, including spot checks.

Mehr also quoted chief nuclear negotiator Ali Larijani as saying Tehran would lift all suspensions on nuclear research if referred or reported to the Security Council.

A joint statement issued after a late-night meeting in London of the foreign ministers of the big five plus Germany and the European Union urged Iran to restore a moratorium on all uranium enrichment-related activity, under IAEA supervision.

Iran, which says its nuclear programme is purely peaceful, announced this month it was resuming nuclear research which had been suspended for two and a half years. It removed UN seals on equipment at its Natanz plant on January 9, but diplomats said there was no sign it had begun uranium enrichment there.

Russia and China had resisted pressure from the United States and its European allies for swift recourse to the Security Council, which has the power to impose sanctions.

Involving the Security Council would mean "the end of diplomacy" to solve the crisis, Larijani told state television.

Russia had argued for the IAEA simply to inform the Security Council about Iran's case, avoiding a formal referral.

However, the White House said it expected the IAEA to refer the Iranian nuclear dossier to the council this week.

"The IAEA board will be meeting on Thursday and we expect the board to refer the matter to the Security Council at that point," White House spokesman Scott McClellan said.

Larijani, who is secretary of Iran's Supreme National Security Council, said his country would respond if it was subjected to severe international pressure.

"If these countries use all their means... to put pressure on Iran, Iran will use its capacity in the region," the semi-official ISNA news agency quoted him as saying.

It was not clear what regional capacities he meant. Analysts and diplomats say Iran, with its links to Islamist parties and militants, has the means to create trouble for the West in Iraq, Lebanon, the Palestinian territories and elsewhere.

Russian Foreign Minister Sergei Lavrov said that although diplomatic pressure on Iran was increasing, the latest decision did not sideline the IAEA in favour of the Security Council.

"We could not support that approach, because the IAEA is continuing its professional work in Iran... and intends to achieve additional results," Russian media quoted him as saying.

Mr Lavrov said Russian and Chinese diplomats would fly to Tehran shortly to urge Iran to answer outstanding IAEA concerns. Russia's Ria news agency said later the Russian team would arrive today.

British Prime Minister Tony Blair hailed the agreement to involve the council as a powerful signal to Iran.

"I hope it's sending a message that the international community is united," Mr Blair said.

Libyan Energy Minister Fathi Omar Bin Shatwan said referral of Iran's case to the council would have a serious effect on world oil prices, already just shy of record highs.

But Iran's Oil Minister Kazem Vaziri eased concerns that the world's fourth biggest crude oil producer could curb oil exports in reprisal, as Tehran has previously hinted it may do.

"We are not mixing oil with politics," he told reporters at the start of an Opec meeting in Vienna.

Iran can count on support at the IAEA meeting from Venezuela and Syria and an abstention from India but the compromise agreed in London is likely to get a comfortable majority in any vote.

A senior British official, who asked not to be named, said Iranian compliance with IAEA demands could defuse the crisis.

"If the Iranians blink there will be no need for any action in New York. That is our preferred option - that Iran heeds the unified message and stops what it is doing," he said.

Javad Vaeedi, deputy head of Iran's Supreme National Security Council, said Iran had no intention of backing down.

"Research and development is the Iranian nation's legitimate right and is irreversible," he told state television.