Russia plans to sign a contract with Iran this year to build two more nuclear reactors at its Bushehr power plant as part of a broader deal for up to eight reactors in the Islamic state, a source close to the negotiations told Reuters on Thursday.
It was not immediately clear how this might affect six global powers' talks with Iran addressing disputed aspects of its nuclear program. Iran has resisted demands for cuts in its uranium enrichment capacity, pointing to plans for a future network of nuclear power stations.
Western powers want any lasting agreement with Iran to put to rest suspicions that it could develop nuclear weapons-making ability through enrichment. Iran denies any such intent.
The talks ended last week with little progress; they are to resume in Vienna in June.
Russia, one of the six powers, built Iran's only operating nuclear power reactor, at Bushehr.
"Russia and Iran may sign an intergovernmental agreement this year on building from four to eight nuclear reactors, and, under the deal, the contract for the construction of the first two reactors as additions to Bushehr," the source said.
Russian state nuclear corporation Rosatom said earlier it was in talks with Iran on the potential construction of more reactors there but revealed no details. Rosatom officials could not immediately be reached for comment on Thursday.
Longstanding Western fears that the Bushehr project could yield spent fuel of use in nuclear weapons - something it denies it is seeking to do - receded after Iran promised to send the material back to Russia.
Moscow voted for four rounds of UN Security Council sanctions against Iran over its contested nuclear activity but has sharply criticized additional measures imposed by the United States and European Union, calling them a hindrance to diplomacy in search of a permanent settlement with Tehran.