The US says it has reached agreement with France, Britain and Germany on a draft UN resolution calling for Iran to end its uranium enrichment programme.
Critics ask why fuel-rich Iran wants nuclear energy too
The text says the UN's atomic agency should decide in November whether to take further action against Iran.
It comes a day after a US nuclear monitor published satellite images of an Iranian weapons facility it said may be used for work on nuclear arms.
Iran dismissed the allegations as lies aimed at deceiving the UN agency.
Diplomats were quoted as saying the US agreed to drop its demands for a 31 October ultimatum to Iran in the agreed new draft resolution.
Instead, it calls on Iran to clear up "outstanding issues" with the International Atomic Energy Agency (IAEA) before the board meets in November.
It asks IAEA boss Mohamed ElBaradei to submit a report reviewing the past two years of inspections in Iran.
And it keeps open the option of "further steps" if Iran fails to comply with IAEA demands, which could include taking Tehran before the UN Security Council for possible sanctions.
The resolution was put forward by Europe's so-called Big Three - Britain, France and Germany. An earlier version proposed by the US, Canada and Australia had sought an October deadline.
The new draft still has to be approved by the IAEA's 35-nation board of governors.
Iran insists its nuclear programme is solely for peaceful purposes.
Isis says Parchin complex shows suspicious structures (photo: DigitalGlobe/Isis)
The issue was thrown into the spotlight again this week with the release of satellite images of the Parchin military complex, south-east of Tehran.
They show buildings that could be used to test nuclear bomb components, the Institute for Science and International Security said.
"This is a new lie, like the last 13 lies based on news reports that have been proved to be lies," Hossein Mousavian, Iran's chief delegate to the IAEA board meeting, said.