Negotiators from three powers and Iran met in Vienna for a third day Wednesday, in an attempt to persuade Teheran to ship most of its enriched uranium abroad.
An agreement would delay Teheran's potential ability to make a nuclear weapon because enriched uranium can be used for the fissile core of nuclear weapons.
The tentative plan envisions Russia enriching the material to a higher grade and then another country turning the uranium into metal fuel rods for Teheran's research reactor.
Iran's interlocutors are the US, Russia and France. The talks opened Monday and have been repeatedly delayed as the two sides search for agreement.