The promise was made in a faxed letter received earlier this week in Vienna by the International Atomic Energy Agency's deputy director for safeguards, Ollie Heinonen, who left Tuesday for Iran.

IAEA officials refused to comment on whether Heinonen, who is expected to return from Iran this weekend, has actually visited Lavizan, where the United States charges that the Islamic Republic did work related to atomic weapons.

Iran tried to acquire equipment that could have been used in uranium enrichment at the Lavizan site, the IAEA said in a report in November 2004.

Iran has removed buildings and topsoil from Lavizan but IAEA officials, who have already visited there, still want to take environmental samples in order to look for traces of uranium particles and want to investigate dual-use machines that were employed at Lavizan, and which could be either for civilian or weapons purposes.

"There was a promise that he would go to Lavizan on this visit. Otherwise, Mr Heinonen would not have traveled to Iran," a diplomat close to the IAEA said.

Heinonen's trip, in a delegation of some six inspectors, gives Tehran a last chance to comply with international inspections, ahead of an emergency IAEA meeting on the Iranian nuclear program in Vienna next Thursday.

Britain, Germany and France called for the emergency meeting of the IAEA board of governors after Iran resumed uranium enrichment work on January 10. Enriched uranium can serve either as fuel for atomic reactors or the raw material for nuclear weapons.

The European trio and the United States want to take Iran before the UN Security Council, which has enforcement powers such as sanctions, in order to put pressure on Tehran to cease all nuclear fuel work and to comply fully with a now three-year-old IAEA investigation into an Iranian atomic program which the United States charges hides secret weapons work.

Diplomats have told AFP that Iran may have received in 1997 three sophisticated P-2 centrifuges, which are machines capable of enriching uranium, from the black-market network of disgraced Pakistani nuclear scientist Abdul Qadeer Khan.

Iran denies having received imports of such centrifuges.

A diplomat said the IAEA has only recently obtained declassified US intelligence on P-2 centrifuges as well as on alleged work by Iran on adapting missiles for nuclear warheads.

Heinonen is to file a progress report ahead of the February 2 meeting, with a more detailed account coming in March, IAEA chief Mohamed ElBaradei said Monday.

"The Iranians chose their timing well," another diplomat said, referring to Iran making concessions whenever it is faced with an international crackdown.

Diplomats said Iran promised to provide responses to other questions the IAEA says must be answered.

These questions concern offers of nuclear technology and parts Iran received in 1987 and 1994 from the Khan network, which would touch on questions about P-1 as well as P-2 centrifuges.

The IAEA has also asked Iran to supply a document it showed the agency on making hemispheres of uranium metal, objects whose only use is as the core of atom bombs.

"The Iranians have promised to let the IAEA put this document under seal," a diplomat said. The diplomat said the seal would be to keep the document safe but that the IAEA could research the information.

IAEA inspectors routinely seal equipment such as centrifuges to make sure that these instruments are not used for sensitive nuclear work.

The final question concerns Iran's alleged efforts to work directly on making nuclear weapons, such as US intelligence that Tehran worked on putting payloads on missiles in a form that would only make sense for nuclear bombs.

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