Iran has been accused of keeping some of its nuclear activities secret [Photo: Digitalglobe]

A White House spokesman said Washington had "serious concerns" about Iran's nuclear programme - and these were shared by the international community.

Earlier, UN nuclear chief Mohamed ElBaradei criticised Iran's apparent lack of co-operation with inspectors. Tehran says its nuclear programme is for peaceful purposes alone. But the International Atomic Energy Agency is debating a motion condemning Iran.

Under pressure

The resolution - put forward by Britain, France and Germany - deplores Iran's conduct.

The IAEA meeting in Vienna earlier heard Mr ElBaradei say Iran's way of "engaging us on this issue has been less than satisfactory."

The IAEA has been investigating Iran's nuclear programme since a deal was struck last year under which Iran agreed to suspend enrichment activities and accept more intrusive inspections of its nuclear sites in exchange for technology.

The BBC's Bethany Bell, in Vienna, says the IAEA's toughened stance puts that deal under pressure.

Questions remain

Mr ElBaradei said he and his inspectors were unsure how far the Iranian nuclear programme went.

"We still have a central issue and that is whether Iran has declared all of its enrichment activities," he said.

Enriched uranium can be used to make nuclear weapons.

He said there were still questions over the origins of traces of weapons-grade uranium discovered in the country, and the scale of its centrifuge-building programme.

It is essential for the integrity of the safeguards operations that we should bring this issue to a close in the next few months IAEA head Mohamed ElBaradei

Mr ElBaradei said there was no clear proof to back up Washington's claims that Iran is chasing nuclear weapons, but he called on Tehran to be "more transparent and proactive".

He said he would like the matter cleared up within "the next few months".

On Monday the IAEA began a meeting in Vienna to debate a toughly-worded resolution put forward by Britain, France and Germany.

The three countries have traditionally taken a softer line on Iran than the United States, which has called on the IAEA to report Tehran to the UN Security Council.

The European countries' resolution does not go that far, but would censure Iran while calling for further co-operation.

Iran defiant

The draft calls for Iran to freeze additional parts of its nuclear programme, something Iran rejects.

The Iranian Foreign Minister, Kamal Kharrazi, says Iran has to be recognised by the international community as a member of the nuclear club.

Iran says its nuclear activities are purely peaceful and aimed solely at generating electricity.

Iranian MPs have threatened to retaliate if the IAEA pushes them too hard.