The United Nations nuclear
watchdog has agreed a draft resolution criticising Iran's co-operation.
International pressure made Iran open up to nuclear inspections
The text "deplores" Tehran's record of with the International Atomic Energy Agency (IAEA) inspectors.
Iran has sharply criticised the text but says it will continue to co-operate with the IAEA.
Britain, France and Germany drafted the resolution as a compromise after the US wanted to hold Iran to a timetable that could trigger UN sanctions.
Tehran has accused the three of working with its arch-foe Washington, which says Iran is developing nuclear arms.
The resolution, a copy of which has been obtained by the BBC, says: "The board deplores at the same time the fact that overall... Iran 's co-operation has not been as full, timely and proactive as it should have been."
Iran has been accused of keeping some of its nuclear activities secret [Photo: Digitalglobe]
It adds: "[The board] calls on Iran to take all necessary steps on a an urgent basis to help resolve all outstanding questions."
The draft resolution is expected to be formally agreed at a meeting of the IAEA's board of governors on Friday.
Correspondents said the text was couched in strong language by the standards of diplomatic terminology.
But the draft does not contain any deadline or trigger mechanism to set into motion possible sanctions against Iran.
Iranian President Mohammad Khatami has warned that Iran's future co-operation would be jeopardised if the criticism persisted.
But Iran said on Thursday it would continue to work with the UN watchdog despite the resolution's wording.
Iranian delegation chief Hossein Mousavian said Tehran was disappointed with Britain, France and Germany, but added: "We maintain our commitment to cooperation with the IAEA."
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.
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.
The IAEA says there are suspicions still hanging over Iran's nuclear programme, and is calling for more transparency.
It has described the discovery of bomb-grade uranium traces at Iranian facilities, and an Iranian attempt to buy centrifuges to speed up the enrichment of uranium, as a cause for concern.