Britain joins call for meeting on Iran's nuclear programme.
Following talks in Berlin between the so-called E3 foreign ministers, Foreign Secretary Jack Straw said they had agreed to request an emergency meeting of the International Atomic Energy Agency board with a view to referring Tehran to the UN Security Council.
The move follows the announcement that the Iranians were to resume work at its Natanz nuclear enrichment facility.
Mr Straw said that efforts by the E3 to find a diplomatic resolution to the crisis were now deadlocked.
He said: "It is a matter of very great regret ... Iran has decided to turn its back and these negotiations have reached an impasse. In that situation, I think we have no alternative but for the decision which we have reached to call for an emergency meeting of the board of governors of the International Atomic Energy Agency with a view to the involvement then of the Security Council."
Although the Iranians insist they only intend to carry out research at Natanz, the Europeans and the United States fear Tehran is using its civil power programme as a cover for developing a nuclear bomb.
German Foreign Minister Frank-Walter Steinmeier insisted they hoped there could be a diplomatic resolution.
He said: "This constitutes a new phase - but not the end - of our diplomatic efforts at trying to achieve a solution."
It will now be up to the board of governors of the IAEA, the UN's nuclear watchdog, to decide whether to refer the matter to the Security Council, which could consider sanctions.