Nuclear negotiators for Iran, obligated to dispose tons of enriched uranium under an approaching deal, are focusing on a U.S.-backed plan for Iran to send the material to another country for sale as reactor fuel.
The Associated Press said this was confirmed by Diplomats.
While Iran says it does not want nuclear arms, it has more than 8 tons that could be turned into the fissile core of a dozen or more atomic bombs if the material was further enriched to weapons-grade levels.
The export-and-sell option has been floated before, and the diplomats emphasized that the sides have not agreed on that solution in the search for what to do with the low-enriched uranium stockpile.
But negotiators have little time left to make a decision on the issue with a Tuesday target date looming for a deal.
Senior Iranian officials publicly rejected shipping out the material in preliminary negotiations, so Tehran's renewed interest is significant.
The goal of the talks involving the U.S., Britain, China, France, Germany and Russia is a comprehensive deal that would crimp Tehran's capacity to make nuclear weapons in exchange for sanctions relief.
Other options discussed would mean changing the enriched uranium into a form that cannot be used for weapons or shipping it abroad for storage, probably in Russia.
One of the diplomats said Russia was a key candidate in the idea being floated that Moscow would convert the low-enriched material and Iran would get a large share of the profits from any sale.
Iran says it is enriching only to make reactor fuel and for other nonmilitary purposes.
Under the preliminary deal that led to the current negotiations, Iran has eliminated almost all uranium enriched to levels only a technical step from weapons grade. That leaves it with a stockpile enriched to levels much lower than what would be needed to make the core of an atomic bomb.
Still, the fact that the stockpile could be enriched further to the level needed for bombs makes rendering it harmless a chief priority for the U.S. and the other countries.
The two diplomats are familiar with the talks but spoke on condition of anonymity because they are not authorized to discuss the confidential talks.
U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif began meeting Saturday in the Austrian capital in an attempt to advance the negotiations.
Zarif said earlier that a deal was in reach unless the other side presented "excessive demands."
He said U.N. sanctions must be lifted immediately after an agreement, and all other penalties also must be removed. The U.S. and its allies say those conditions are unacceptable.
French Foreign Minister Laurent Fabius said France wants "an accord that is robust that recognizes in Iran the right to civil nuclear but that guarantees that Iran effectively and definitively renounces nuclear arms."
He said Iran has not "completely" accepted France's conditions: long-term limitations on Iran's nuclear research and development; rigorous verification of the deal with few limitations; and "an automatic return of sanctions in case of violations."
Kerry and Zarif spoke of tough negotiations ahead, in comments that added to the likelihood that the talks will slide into early July.
"We need to work really hard in order to be able to make progress," Zarif said.
Kerry spoke of "some very tough issues" in the way of a deal, adding: "We have a lot of hard work to do."