On Wednesday Tony Blair, the British prime minister, said an emergency meeting of an EU troika in Berlin on Thursday would weigh up its response to the crisis but that it was "likely" to end in Iran's referral to the UN body.
It followed the Islamic republic's declaration on Tuesday that it was ending a two-year suspension of nuclear fuel research, sparking a furious reaction from the US, the European Union and a host of other countries.
Russia, which has been a frequent ally of Iran over its nuclear programme, hardened its rhetoric, saying the resumption was "cause for alarm".
Central to the concerns of the international community is that Tehran could be trying to develop atomic weapons, a charge Iran strongly denies, insisting the programme is for entirely civilian purposes.
Mahmoud Ahmadinejad, the Iranian president, vowed not to be intimidated by the "fuss" and said he hoped atomic energy would soon "serve the progress" of the country.
Rafsanjani has come out in open
support of Ahmedijad's stand
"I am telling all the powers that the Iranian nation and government, with firmness and wisdom, will continue its path in seeking and utilising peaceful nuclear energy," he told supporters in the southern 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."
Akbar Hashemi Rafsanjani, Iran's influential former president, 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," said the head of the Expediency Council, Iran's top political arbitration body.
The meeting in Berlin will gather the foreign ministers of Britain, France and Germany, which have been negotiating with Iran over its programme.
"The first thing to do is to secure agreement for a reference to the (UN) Security Council, if that is indeed what the allies jointly decide, as I think seems likely," Blair told the British parliament.
"If the regime in Iran continues on the current course ... there is no other choice but to refer the matter to the (UN) Security Council"
White House spokesman
Frank-Walter Steinmeier, the German foreign minister, said the participants would consult afterwards with Condoleezza Rice, US secretary of state, by telephone.
Steinmeier said the purpose was to decide whether there was still "political room to manoeuvre" between the European troika and Tehran.
"If the regime in Iran continues on the current course ... there is no other choice but to refer the matter to the (UN) Security Council," said Scott McClellan, the White House spokesman.
Referral to the Security Council normally pass through the International Atomic Energy Agency (IAEA).
US officials had privately made no secret of their scepticism over the EU's negotiating efforts, but now appear convinced that Washington's tactic of letting the talks run their course has borne fruit in highlighting Tehran's intransigence.
A Western diplomat in Vienna said there was talk of a special board meeting of IAEA governors in about two weeks.
Tehran upped the stakes in its lengthy confrontation with the international community on Tuesday when it broke the seals at its Natanz nuclear plant in order to resume research into uranium enrichment.
"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"
Seals there and at two other plants were being broken, the IAEA confirmed, with Mohamed ElBaradei, the IAEA chief, saying Iran had explained that it planned to start "small-scale" uranium enrichment at Natanz.
Enriched uranium can be used in nuclear-power stations but, in highly enriched form, can be used also for atomic weapons.
Sergei Ivanov,the Russian defence minister, declined to speculate on whether the growing confrontation would lead to action by the Security Council, but said things were not moving in a positive direction for anyone.
For his part, Ehud Olmert, the acting Israeli prime minister, says Iran should be referred to the UN body "as soon as possible."
Israel was "concerned about developments in Iran including statements by its leaders regarding Israel", his office reported him as saying in reference to recent remarks by Ahmadinejad questioning Israel's right to exist.