Iran signaled ahead of international talks on Monday that it will not meet Western demands for a deal that would move most of its enriched uranium out of the country and delay its gaining the ability to make a nuclear bomb.
Tehran says it needs enriched uranium for nuclear fuel, but the West fears it could be used for weapons. The US says Iran is now one to six years away from being able to make such arms, should it choose to.
Tehran's refusal to give up most of its enriched stock could doom both Monday's talks and chances of a second round of broader negotiations between Tehran and six world powers on the Islamic Republic's nuclear program.
Monday's Vienna talks between Tehran and the US, Russia and France, focus on a technical issue with huge strategic ramifications _ whether Iran is ready to farm out some of its uranium enrichment program to a foreign country.
Progress would strengthen confidence on the part of the US and five other big powers trying to persuade Iran to dispel fears about its nuclear program that this time Tehran is serious about reducing tensions and ready to build on Oct 1 Geneva talks with six world powers.
Beyond that, it could give the international community more negotiating space by delaying Tehran's ability to turn what is now a civilian uranium enrichment program into an assembly line producing fissile warhead material.
The talks Monday will attempt to implement what Western officials say Iran agreed to during the Geneva talks; letting a foreign country _ most likely Russia _ turn most of its low-enriched uranium into higher grades to fuel its small research reactor in Tehran. That would mean turning over more than 1,200 kilograms of low-enriched uranium _ more than 2,600 pounds and as much as 75 per cent of Iran's declared stockpile. Tentative plans are for further enrichment in Russia and then conversion in France into metal fuel rods for the Tehran reactor.
Iran's state-run Press TV cited unnamed officials in Tehran as saying the Islamic Republic was looking to hold on to its low-enriched uranium and buying what it needed for the Tehran reactor abroad.
Such a stance would likely doom the talks, with neither the US or France accepting such terms.
Iranian agreement to such terms would be significant because 1,000 kilograms is the commonly accepted threshold of the amount of low-enriched uranium needed for production of weapons-grade uranium enriched to levels above 90 percent.
Based on the present Iranian stockpile, the US has estimated that Tehran could produce a nuclear weapon between 2010 and 2015, an assessment that broadly jibes with those from Israel and other nations tracking Tehran's nuclear program.
If most of Iran's declared stock is taken out of the country, further enriched abroad and then turned into fuel for the Tehran reactor, any effort to make nuclear weapons would be delayed until Iran again has enriched enough material to turn into weapons-grade uranium.
"It buys some time," said David Albright of the Washington-based IISS, which has closely tracked Iran for signs of any covert proliferation. But Albright added that Iran could replace even 1,200 kilograms of low-enriched uranium "in little over a year" at its present rate of enrichment.
And ahead of the talks it remained unclear whether Iran was even ready to discuss shipping out most of its enriched stock. A senior Western diplomat in Vienna who is familiar with Monday's talks told The Associated Press shortly before they were to begin that the Iranians had not communicated any refusal to discuss transferring their enriched uranium to the delegations involved in the negotiations.
Even if Tehran agrees, it could still try to resist pressure to hand over most of its stock in one batch, insisting instead on sending small amounts out of the country. Iran still has enough fuel for the Tehran reactor to last until mid-2011.
With more than 4,000 centrifuges now producing low-enriched uranium, and its capacities increasing, that could leave Tehran in a position to rapidly make up for amounts exported to again amass enough material to make one nuclear weapon.
The six powers _ the US, Russia, China, Britain, France and Germany _ have tentatively scheduled follow-up talks to the Geneva meeting by the end of this month aimed at starting negotiations that will ultimately place strict controls on Iran's enrichment activities.
But no date has been announced for those talks, with the six nations awaiting the results both of the Vienna meeting and a planned Nov. 25 IAEA inspection of an enrichment plant being built near the holy city of Qom. Iran informed the IAEA of the plant in a confidential letter just days before President Barack Obama and the leaders of France and Britain jointly told the world of its existence and denounced Iran for keeping it secret.