Diplomats say Iran and the US have tentatively agreed that Tehran will ship to Russia much of the material it could use to manufacture nuclear weapons.
The two diplomats also say that negotiators at the nuclear talks in December were for the first time able to draw up a catalogue that outlines areas of potential accord and differing approaches to remaining disputes.
Differences still dominate ahead of the next round of Iran-six power talks on January 15 in Geneva, the diplomats recently said.
They demanded anonymity because they are not authorised to discuss the closed negotiations.
Iran denies it wants nuclear arms.
The two diplomats also say that negotiators at the nuclear talks in December were for the first time able to draw up a catalogue that outlines areas of potential accord and differing approaches to remaining disputes.
Differences still dominate ahead of the next round of Iran-six power talks on January 15 in Geneva, the diplomats recently said.
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But they suggested that even agreement to create a to-do list would have been impossible in previous rounds because of the wide gap between the two sides.
They demanded anonymity because they are not authorised to discuss the closed negotiations.
Iran denies it wants nuclear arms.