The UN nuclear watchdog will host talks between Russia, France, the United States and Iran in Vienna on Monday that are seen as crucial to resolving the long-running standoff over Tehran's disputed nuclear drive.
Officials from Moscow, Paris, Tehran and Washington will meet at the International Atomic Energy Agency's headquarters in Vienna, to work out the modalities for a deal allowing the Islamic Republic -- which the West accuses of seeking to build an atomic bomb -- to secure nuclear fuel for a research reactor.
The reactor, which makes isotopes for medical uses such as cancer treatment, runs on uranium enriched to 19.75 per cent, a level not so far achieved by Iran by itself.
Until now, the fuel has come from a batch of around 116 kilogrammes (2555 pounds) purchased by Iran from Argentina back in 1993, which is now running low.
As part of its controversial atomic drive, which the US in particular charges is a cover to build a bomb, Iran has managed to produce by itself uranium enriched to levels of no more than 5.0 per cent.
Iran insists its nuclear activities are entirely peaceful and so-called low-enriched uranium (LEU) is indeed used to produce fuel for civilian nuclear reactors. But when enriched further -- to 90 per cent and more -- uranium can also be used to make the fissile core of an atomic bomb.
The West is concerned that if Iran enriches still further the stockpile of around 1,500 kilogrammes of LEU that it has so far amassed at its plant in Natanz, it will bring it closer to levels needed to make weapons-grade material.
According to Western diplomats, Iran contacted the IAEA in June to tell it that the current batch of fuel for the reactor would run out by the end of 2010, and asked the watchdog if it could find a country that would sell it some more.
The IAEA responded in September with a plan whereby Iran would hand over its stockpile of LEU to Russia to enrich it to the level required to run the research reactor.
Another country, France, would then take the enriched fuel and fashion it so that it could be used in the reactor, said a European expert with knowledge of the dossier.
"It's a win-win situation," one Western diplomat said.
The Iranians would get the fuel they needed, while at the same time, Western fears would be alleviated that the material could be used to make a bomb.
At rare high-level talks with six world powers in Geneva in October, Iran agreed to buy the higher grade uranium required from overseas suppliers.
"This meeting in Vienna is now an opportunity to show that they're serious, that they're willing to follow through on that," another diplomat said.
"The Iranians made this proposition, now it remains to be seen whether they say 'yes'," said yet another diplomat.
It is not yet clear exactly who will be attending the meeting, what will be concretely discussed and what outcome can be expected.
All the IAEA has said is that the talks will begin at 3:00 pm (1300 GMT) on Monday and "may extend through Tuesday and Wednesday."
Diplomats said that, contrary to expectations, Iran will not be sending its atomic chief Ali Akbar Salehi.
If he does not attend, that could be seen by the West as a sign that Iran is not really serious, a diplomat said.
Iran for its part has warned that it would go ahead and enrich uranium on its own if the deal failed.
Last week, the Iranian news agency ISNA quoted the spokesman of the Iran Atomic Energy Organisation, Ali Shirzadian, as saying: "We will write a letter and announce (to the IAEA) that Iran will act directly to supply the fuel for the Tehran reactor."
Shirzadian said the reactor needed around 200 kilogrammes of medium-enriched uranium to operate, but did not say how long that would last.
And the fact that Iran "fully owns the enrichment technology" will give it "leverage ... at the negotiating table," he said.
Nevertheless, Iran would prefer to "buy the fuel for the Tehran reactor in bulk as it is more economical," Shirzadian added.