The United Nations' nuclear watchdog has adjourned a meeting on Iran's nuclear programme as diplomats struggle to find a common position.
Iran denies it is developing nuclear weapons
The agency's director-general, Mohamed ElBaradei, said the board needed more time to work out its response to his latest report on the programme.
Washington is calling for strong condemnation of Tehran for its failure to report its activities for 18 years.
But European countries, including the UK, are taking a softer line.
US negotiators appear to have dropped demands that Iran be reported to the UN Security Council.
This could have led to the imposition of sanctions on Iran.
The US has accused Iran of covertly seeking to develop nuclear weapons, a charge Tehran strongly denies.
Mr ElBaradei said the International Atomic EnergyAgency (IAEA) would reconvene its meeting on Wednesday, with only the issue of the response to be resolved.
"By that time we will have a draft resolution hopefully to be adopted, I still believe, by consensus," he said.
He added that the board had formally approved Iran's intention to sign up to tougher inspections of its nuclear programme.
But Iran has indicated it may re-consider signing this additional protocol if the board issues a resolution saying that it has not complied with the nuclear Non-Proliferation Treaty (NPT).
In his report, Mr ElBaradei said that Iran had secretly produced plutonium and enriched uranium - materials which can be used in nuclear weapons.
Iran has admitted to some violations in the past but says its nuclear programme is peaceful.
Britain, France and Germany have reportedly been proposing that the IAEA "strongly deplore Iran's past breaches", after an earlier draft seeking Iran's continued co-operation with the IAEA was criticised by the US as too weak.