European powers have drafted a new resolution for the UN nuclear watchdog that rebukes Iran but refrains from directly threatening sanctions.
International pressure made Iran open up to nuclear inspections
The draft written by France, Germany and Britain is expected to be amended before formal submission in a few days.
Tehran has accused the three of working with its arch-foe Washington, which says Iran is developing nuclear arms.
President Mohammad Khatami warned that Iran's future co-operation would be jeopardised if the criticism persisted.
"Continuation of such behaviour, under US pressure, will seriously harm mutual confidence and Iran's co-operation with the international community for the peaceful use of nuclear energy," Mr Khatami is quoted as saying.
Iranian officials have not elaborated on the comments, which came in a letter to France, Germany and Britain published in the Iranian press on Tuesday.
Correspondents who have seen the latest International Atomic Energy Agency (IAEA) draft resolution say one key phrase "deplored" the fact that Iran's co-operation "has not been complete".
This is considered strong terminology in diplomatic language.
But the draft does not contain any deadline or trigger mechanism to set into motion possible sanctions on Iran.
Iran has been accused of keeping some of its nuclear activities secret [Photo: Digitalglobe]
Washington has suggested the IAEA should report Tehran to the UN Security Council for allegedly secretly developing nuclear weapons which could lead to formal sanctions.
There is one accommodation to Iran in the draft, however - a softening of language about a proposed heavy-water reactor that would produce bomb-grade plutonium.
The new version asks Iran to "reconsider" its plans, having previously called for the decision to continue the programme to be reversed.
Under growing international pressure, Iran has suspended uranium enrichment and allowed the IAEA to inspect its nuclear facilities without notice.
But Tehran rejects US allegations that its nuclear programme is being used to make weapons and says it is solely for generating electricity.
An IAEA report published in April said suspicions still hung over the programme.
It said the discovery of bomb-grade uranium traces at Iranian facilities, and an Iranian attempt to buy centrifuges to speed up the enrichment of uranium, were a cause for concern.