Iran, which denies any interest in such weapons, currently runs over 10,000 centrifuges that have created tons of fuel-grade material that can be further enriched to arm nuclear warheads. That's a relatively slow process with such reactor-grade material.
But Tehran also has nearly 440 pounds (200 kilograms) of higher-enriched uranium in a form that can be turned into weapons much more quickly. Experts say 550 pounds (250 kilograms) of 20 percent-enriched uranium are needed to produce a single warhead
The following is a list of demands on Iran from the six powers the United States, Russia, China, Britain, France and Germany and what the diplomats say Tehran offered at the Geneva talks:
SUSPENSION OF ENRICHMENT ABOVE REACTOR FUEL-GRADE LEVELS
The six want Iran to stop enriching uranium to 20 percent. The diplomats say Iran offered to halt 20-percent enrichment at the Geneva talks, which ended Wednesday. They had already proposed this at the round preceding the Geneva talks.
ENRICHMENT AT FORDO
The six demand that enrichment operations at Fordo, an underground bunker believed to be impervious to air strikes, be disabled to the point where they would be difficult to restart. The diplomats say Iran offered only to discuss the status of Fordo.
LIMITS ON ALL IRANIAN ENRICHMENT
The six powers want a cap on how much enriched material Iran can produce and stockpile. With some of Iran's enriching centrifuges more efficient than others, this would mean tough negotiations on the number and type of machines it has installed and is operating. The diplomats say Iran has signaled it is open to discussing numbers.
URANIUM STOCKPILES
The six powers want Tehran to ship out most of its supply of 20-percent enriched uranium or blend it down into reactor fuel. They also want Iran to agree to stricter U.N. supervision of its lower-grade enriched uranium stockpile. The diplomats said the Iranians did not substantially address these demands.
Additionally, the diplomats said the Iranians agreed to discuss six power concerns about a reactor that experts say will produce enough plutonium for one or two bombs a year once completed. The U.S. and its allies have called on Tehran to stop construction of that reactor.
Araghchi predicted Monday the nuclear talks could take as long as a year in step-by-step measures with the first milestone coming in three to six months and negotiations concluding within the year.
Such as a timetable, however, could bring pressure on Washington from Israel and others that fear Iran could be seeking to buy time while making nuclear advances. The diplomats said no formal implementation time table of any deal was discussed last week.
In contrast to the overture on nuclear efforts, hardline factions in Iran have increased their bluster. They hold sway over the pace and direction of the nuclear program and the West could grow increasingly skeptical about the country's outreach.
On Tuesday, Gen. Masoud Jazayri, the deputy chief of staff of Iran's armed forces, issued a veiled warning to the negotiators representing Tehran at the talks.
"Iranian diplomats will never give in to the oppressive West," Jazayri was quoted as saying by the semi-official Fars new agency. "The Iranian people will carefully watch what their own representatives and the other party at the talks say and do."
Experts from both sides are to meet at a yet unannounced date before the next round of talks in Geneva Nov. 7-8. The diplomats said that only if that meeting makes progress in nailing down concrete issues to be negotiated at the Geneva talks can last week's round be called a success.
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Associated Press writers Brian Murphy in Dubai and Nasser Karimi in Tehran contributed to this report.