Pressure mounted on Iran to agree to a UN-brokered nuclear deal on Friday which could ease fears the Islamic Republic is seeking atomic weapons.

France, Russia and the United States all gave their backing to a plan, drafted by the International Atomic Energy Agency earlier this week, under which Moscow would enrich the uranium that Tehran needs for a research reactor.

Iran has yet to respond to the proposal.

But French Foreign Minister Bernard Kouchner, on a trip to Beirut, said the signs coming from Iran so far were "not positive".

IAEA chief Mohamed ElBaradei had set Friday as the deadline for all parties to sign off on the arrangement which was aimed at breaking the seven-year deadlock on the Iran's suspect nuclear programme.

ElBaradei did not specify a definite time when he set the deadline, but theoretically, Iran has until midnight to respond.

Russia was the first of the four countries to formally back the proposal.

It was followed by France and the United States.

"The United States delivered its positive response to IAEA Director General's (Mohamed) ElBaradei's proposal," said National Security Council spokesman Mike Hammer. "We look forward to Iran's reply."

In Paris, French foreign ministry spokesman Bernard Valero agreed that the draft agreement "suits" Paris.

"We have made this known in an official manner," Valero said, adding that ElBaradei was awaiting "a clear response from Iran."

Nevertheless, in Tehran, an Iranian source close to the Vienna talks was quoted as saying on state television's website that the Islamic Republic was awaiting a "positive" response from world powers over its own proposal to procure nuclear fuel for the research reactor.

"Iran is the buyer of nuclear fuel for the Tehran reactor and sellers must give a positive response to the buyer's proposal and not consider their own view as a positive response," the source said, adding that Iran "entered the Vienna talks with a positive and constructive approach, and now it is awaiting a constructive response and positive response to Iran's proposal."

The other parties "are expected to give a response which builds confidence and is constructive in return for the transparency and goodwill of the Islamic republic," the source said.

The comments were seen as sign that Iran's intention was to drag out the negotiations beyond Friday, a move which western diplomats said the other countries would not accept.

In Beirut, French foreign minister Kouchner said: "The signs we received (from Iran) this morning are not positive. It is a pity. The day is not over, and I still have hope, but (Iran's refusal) would be unfortunate for the talks in Vienna."

Uranium enrichment lies at the heart of Western concerns about Iran's nuclear programme. It produces fuel for civilian reactors, but in highly extended form can also make the fissile core of an atomic bomb.

On Saturday, IAEA inspectors are set to fly out to Iran to inspect a hitherto underdeclared second uranium enrichment plant near the holy city of Qom.

According to the official IRNA news agency, inspectors "will stay for two or three days" in Iran.

Iran's hardline Islamic regime denies Western allegations it is seeking to build an atomic bomb, but has however given mixed signals over whether it is ready to send virtually all of its uranium abroad, as proposed in ElBaradei's arrangement.

The full details of the deal have not been released. But France has said the draft agreement calls on Iran to hand over 1,200 kilogrammes of low-enriched uranium (LEU) it has at its Natanz plant -- in defiance of UN sanctions -- to Russia by the end of the year.

Russia would enrich the material to the 19.75 percent needed to use it in a research reactor that makes radio-isotopes for medical use.

Diplomats say Russia would then sub-contract to France the process of turning the enriched uranium into the fuel rods for the reactor.

Iran insisted Thursday that it would not halt its enrichment work at Natanz even if it approves the deal with Russia.

"There is actually no need for us to enrich uranium to more than four or five percent purity as the reactors that we use need uranium enriched to a maximum of five percent," said Ali Akbar Salehi, head of Iran's Atomic Energy Organisation.

"But that does not mean that we will renounce our right to enrich uranium level to a higher level. Iran has the capability to enrich uranium to 20 percent but prefers to obtain the fuel from abroad," Salehi said.