The permanent UN Security Council members have closed ranks at the emergency session in Vienna of the watchdog International Atomic Energy Agency by supporting a draft resolution to take Iran to the Council over a nuclear programme the United States charges hides secret atom weapons development.
The text is a compromise between a US desire for immediate Council action against Iran and Russia's demand for a month's time, until the next IAEA meeting in March.
ElBaradei told reporters that the showdown over Iran was "reaching a critical phase, but it is not a crisis situation."
Iran's nuclear programme "is not about an imminent threat. I should make that very clear."
Russia, a key trade partner of Iran, hopes diplomatic efforts can convince Tehran to respond to IAEA edicts for it to suspend nuclear fuel work and cooperate fully with agency inspectors.
Russian Ambassador Gregory Berdennikov said clearly "yes" when asked by reporters if he would vote for the draft text and China is expected to follow the Russian lead, a Western diplomat said.
Iran reacted, however, with threats to move ahead on uranium enrichment, the crucial technology that makes nuclear reactor fuel that can also be bomb material, and to reduce co-operation with the IAEA if the agency went ahead with referral when its meeting resumes on Friday.
Top Iranian nuclear negotiator Ali Larijani said in a letter to IAEA Chief Mohamed ElBaradei: "In that case the agency's monitoring would extensively be limited and all the peaceful nuclear activities being under voluntary suspension would be resumed without any restriction."
The IAEA has called on Iran to suspend all nuclear fuel activities but Iran pressed ahead in January with uranium enrichment, after having in August resumed uranium conversion that makes the feedstock gas for enrichment.
Iran's hard-line President Mahmoud Ahmadinejad vowed on Thursday his country would "under no condition" abandon its disputed nuclear drive.
"The main thing in nuclear energy is enrichment," Ahmadinejad said.
In Washington, US National Intelligence Director John Negroponte said Iran probably does not yet have a nuclear weapon and does not have the necessary material for one.
A vote at the IAEA's board of governors is not expected until Friday, giving time for Europe and the United States to lobby for wide support.
US critics, Cuba, Syria and Venezuela, said they would vote against referral, but the resolution written by Britain, Germany and France is expected to meet the US goal of rallying some 30 of the board's 35-member states.
Diplomats said non-aligned states, which back Iran's right to the peaceful use of nuclear energy and have doggedly fought referral in the past, were surprised by the position of Russia and China.
The NAM were trying to amend the resolution, but diplomats said the Europeans would not budge on the key clauses about Security Council referral.
US Ambassador Gregory Schulte insisted Europe and Washington still wanted a diplomatic resolution.
Referral to the world body "will increase the diplomatic tools available to the Council," he said, adding that the United States "continues to support all efforts to seek a peaceful diplomatic solution."
The United States has sought backing for two years for taking Iran to the Council, which unlike the IAEA has enforcement powers.
But Washington has also supported a proposal by Moscow to resolve the row by having Iran enrich uranium in Russia, preventing Tehran mastering the key technology.
The Vienna-based IAEA has been investigating Tehran for three years, and in September found it in non-compliance with the Non-Proliferation Treaty (NPT) for hiding sensitive nuclear activities for 18 years.
Such a finding requires a report to the Security Council, but the IAEA held off on this to give Iran time to cooperate with the agency's investigation and stop nuclear fuel work.
Instead, Iran moved on January 10 to start uranium enrichment work and has not fully co-operated with the IAEA inspectors, according to an agency report.