Diplomats at the Russian Embassy in Tehran today handed over a formal note to Iranian officials stating that its earlier offer to create "on Russian soil a joint Russo-Iranian undertaking to enrich uranium" remains in force.
Tehran had previously rejected the proposal, despite friendly ties with Russia, which is building Iran's first nuclear reactor.
Moscow's persistence adds to Western pressure on Iran to forgo a complete nuclear fuel cycle the West says could be used to make weapons of mass destruction.
Iran says its nuclear program is only for peaceful purposes.
EU negotiators Germany, Britain, and France this week (on 21 December) restarted talks with Iran on the issue. They agreed to meet again in January.