US Secretary of State Condoleezza Rice will host her counterparts from Britain, China, France, Germany and Russia as well as European Union foreign policy chief, Javier Solana, at a working dinner that will focus on Tehran's rejection of repeated UN demands to halt uranium enrichment.

The meeting will coincide with continuing bargaining in the 15-member UN Security Council on a Franco-British draft resolution that would legally require Iran to freeze all uranium enrichment and reprocessing activities.

It comes as an Iranian government spokesman said President Mahmoud Ahmadinejad had written a letter to US President George W. Bush to "propose new ways" to resolve tensions.

"President Ahmadinejad has written a letter to George Bush, which is to be handed to the Swiss embassy," Gholam Hossein Elham told reporters in Tehran.

It is the first time an Iranian president has been known to officially communicate with an American president since Washington and Tehran cut off diplomatic relations in 1980.

"In this letter, while analysing the world situation and finding the roots of the problems, he has proposed new ways for getting out of the existing vulnerable world situation," the spokesman said.

French President Jacques Chirac and German Chancellor Angela Merkel issued a joint call for a tough UN stance Sunday, saying the Security Council must adopt "a resolution making obligatory the requests of the IAEA ( International Atomic Energy Agency), notably the suspension of uranium enrichment," according to the French president's office.

US Ambassador to the UN John Bolton told reporters Saturday that the ministers would "talk about the longer-term policy that we need to pursue to stop Iran from achieving a nuclear weapons capability" at Monday's meeting.

Western powers suspect Iran is using its civilian atomic program as a cover to develop nuclear weapons. But Iran insists its aims are peaceful and claims it has the right to pursue uranium enrichment as a signatory to the nuclear Non-Proliferation Treaty.

While insisting that it wants a diplomatic solution to the standoff with Tehran, Washington has not ruled out military action to prevent Iran from acquiring nuclear weapons.

Moscow and Beijing object to the draft's reference to Chapter Seven of the UN charter and its suggestion that the Iranian nuclear program constitutes a threat to international peace and security.

Chapter Seven can authorize economic sanctions or military action as a last resort.

The proposed draft would oblige Iran to suspend uranium enrichment, the process creating fuel for nuclear reactors and -- potentially -- the core of an atomic bomb. It warns, in case of Iranian non-compliance, of unspecified "further measures" requiring another resolution.

The document needs at least nine votes and no veto from any of the council's permanent members to succeed.

But Iran shows no sign of backing down.

"The involvement of the Security Council will direct the path of cooperation towards confrontation," Iranian foreign ministry spokesman Hamid Reza Asefi said Sunday, warning that the Security Council would not be able to enforce its demands.

And Russia and China say the nuclear standoff can only be resolved diplomatically, with the IAEA leading the process.

In an interview with the German television channel ARD broadcast Sunday, US President George W. Bush said the standoff must be resolved "diplomatically," adding that there must be "a common front with a common strategy" to achieve the objective.