The British, French and German foreign ministers were to discuss their response yesterday after Iran veered closer to UN action by pledging to continue sensitive nuclear research.
The three EU countries have been seeking a negotiated solution for two years but both Britain and the US have warned that Iran was now likely to be referred to the UN Security Council for possible sanctions.
Iran broke the UN seals at its Natanz nuclear plant on Tuesday to resume research into uranium enrichment, prompting a furious reaction from world leaders who fear Tehran is trying to develop nuclear weapons.
Iran insists its program is only for civilian purposes.
British Prime Minister Tony Blair said Iran was now likely to be referred to the Security Council, and there was also a strong reaction from the US and the EU.
Iranian President Mahmoud Ahmadinejad vowed not to be intimidated by the "fuss" and said he hoped atomic energy would soon "serve the progress" of Iran.
"I am telling all the powers that the Iranian nation and government, with firmness and wisdom, will continue its path in seeking and utilizing peaceful nuclear energy," he told supporters in the city of Bandar Abbas. "In the path of nuclear energy, we have started [nuclear fuel] research and God willing, in the near future this energy in its entirety will serve the Iranian nation."
Former Iranian president Akbar Hashemi Rafsanjani, now head of the nation's top political arbitration body, was even more forthright.
"With wisdom we will get our rights, and if they create any trouble for us, they will regret it in the end and Iran will emerge triumphant," he said.
US Vice President Dick Cheney said referral to the Security Council would be the probable next step.
"What would be probably the number one item on the agenda would be [a UN] resolution that could be enforced by sanctions, were they to fail to comply with it," Cheney said on US radio.
State Department spokesman Sean McCormack said: "It is more likely than ever that we are headed to the Security Council on this question."
McCormack said US Secretary of State Condoleezza Rice conferred by phone with British Foreign Secretary Jack Straw and also with Mohamed ElBaradei, head of the UN's International Atomic Energy Agency (IAEA).
UN Secretary-General Kofi Annan said he was "very concerned" over Iran's activity, but added that it was up to the IAEA to deal with the matter, spokesman Stephane Dujarric said.
Annan was "very appreciative" of the efforts of the so-called EU-3 and Russia to find a diplomatic solution to the crisis, Dujarric said, but felt that "at this point" the IAEA and the EU members "remain clearly in the lead in this situation."
Even Russia, a frequent ally of Iran, highlighted its concern at Iran's latest nuclear action.
Foreign Minister Sergei Lavrov called the breaking of the seals a "cause for concern," while Defense Minister Sergei Ivanov said the move "personally disappoints me and gives some cause for alarm."
The crisis has hit world energy markets. Oil prices continued higher in Asian trade yesterday with Iran's defiant stand sparking unease, dealers said.
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