The UN's nuclear watchdog has begun meeting to decide whether to report Iran to the UN Security Council - a move which could lead to sanctions.
Iran threatens to resume suspended nuclear activities
The Vienna-based body is considering a resolution agreed by the five permanent Security Council members plus Germany.
If reported, Iran says it will resume uranium enrichment and end UN checks.
Correspondents say there is no sign of an early vote, and the meeting may continue on Friday as many board members want to express their views.
Diplomats have said the 35-member board will easily pass the resolution, and Russia has re-affirmed its intention to back it after Iran insisted it had Moscow's support.
Analysts say the text of the resolution is a compromise that puts off any UN action, including possible sanctions, until at least March, when a conclusive report is delivered by the head of the International Atomic Energy Agency (IAEA).
The six powers - Britain, the US, France, China, Russia and Germany - agreed the resolution on Monday.
It was however edited over the next two days, with Russia insisting it should not specifically refer to UN statutes that would authorise sanctions.
The US said it was supporting the compromise to show it wanted a political settlement and to build an international consensus on the issue.
The US ambassador to the IAEA, Gregory Schulte, said the draft "has the support not only of the European Union but also of the United States, also of Russia, also of China and also of a large number of other countries".
Russia's chief delegate confirmed this at the meeting.
""We do not object to informing the Security Council of the United Nations about the work carried out by the agency in relation to Iran," Grigory Berdennikov said.
But Iran's ambassador to the IAEA, Ali Soltanieh, told the BBC earlier he was sure Russia and China would side with Iran.
"They are not going to support [the draft] because they know how essential the bilateral relations that we have with China and Russia are, therefore Russians know how serious we are for constructive discussion on the Russian proposal for enrichment," he said.
The resolution reads: "[We] call on Iran to understand that the board lacks confidence in its intentions in seeking to develop a fissile material production capacity against the background of Iran's record on safeguards."
It also urges Iran to extend "indispensable and overdue" co-operation to the IAEA and help it "clarify possible activities which could have a military dimension".
One diplomat told Agence France-Presse the military reference was new, adding: "It's calling a spade a spade, and that's good."
On Wednesday, President Ahmadinejad gave a defiant speech on state TV, saying Iran would never give up its "right" to peaceful nuclear energy.
Hours earlier, US President George W Bush was equally strident in his State of the Union address, saying Iran should not be permitted to get nuclear weapons.
Western powers are concerned about Iran's recent decision to resume suspended research on uranium enrichment - a process that can lead to a nuclear weapons capability.
Iran says its programme is solely aimed at energy production.
It has threatened to resume uranium enrichment and end snap UN inspections of its nuclear facilities if it is reported to the Security Council.