The UN's nuclear watchdog has put off until Saturday a meeting on whether to report Iran to the UN Security Council.
Iranians have been demonstrating in support of their country
Diplomats believe the motion to report Tehran over its nuclear activities - which the EU and US say still leaves room for diplomacy - will be passed.
No reason has been given for the delay. Russia has reportedly decided to back the move if the threat of sanctions is withheld for at least another month.
Iran's former leader said sending it to the UN would be a historic injustice.
Speaking at Friday prayers, ex-President Akbar Hashemi Rafsanjani said there were better ways to resolve the issue and warned that reporting Tehran would be a "black page" in history.
Iran's top nuclear negotiator, Ali Larijani, said Tehran would stop allowing UN inspections and resume peaceful nuclear activities "without restriction" if Iran was sent to the Security Council, which has the power to impose sanctions.
Iran recently decided to resume suspended research on uranium enrichment.
This has not yet led to full-scale uranium enrichment - a process that creates fuel for nuclear reactors and, potentially, for a nuclear bomb - but Western powers are concerned.
Iran maintains its programme is for producing energy and does not have a military aim.
'Window of opportunity'
The 35-member board of the UN watchdog, the International Atomic Energy Agency (IAEA), had been due to reconvene on Friday afternoon in Vienna for the second day of its emergency meeting on Iran.
But the scheduled meeting was first delayed and then postponed until Saturday morning, following a day of backroom diplomacy.
An EU diplomat earlier told Reuters news agency that supporters of sending Iran to the Security Council thought they had the votes to succeed.
EU foreign policy chief Javier Solana said China, which has previously urged diplomacy, had agreed to back Europe on the motion.
The head of the IAEA, Mohamed ElBaradei, has said the row over Iran's nuclear research is reaching a critical phase but Tehran has a "window of opportunity".
He says the Security Council members have made it clear no action that might lead to sanctions should take place before March, when he is to submit a conclusive report.
"All of them are saying that this is simply a continuation of diplomacy," Mr ElBaradei said.
16 Feb, Moscow: Russia and Iran resume talks on Russia's proposed compromise
March, Vienna: IAEA to report on Iranian compliance; possible Security Council action to follow
The resolution to be considered urges Iran to extend "indispensable and overdue" co-operation to the IAEA and help it "clarify possible activities which could have a military dimension".
Russian had argued that the IAEA motion must not contain any immediate threat of sanctions against Iran.
Moscow, a major trading partner of Tehran's, has offered to enrich uranium for Iran on its own soil.
The proposal is designed to give Iran the fuel it wants while easing fears that it could be diverted to bomb-making.
However, Iranian negotiator Javad Vaeidi warned on Friday that reporting Iran to the UN would "kill" any chance of the Russian compromise deal going ahead.
Russian and Iranian officials are expected to meet on 16 February to discuss the proposal.