Russia has signed a preliminary agreement to build at least two more nuclear power plants in the Iranian port city of Bushehr, Iran's official IRNA news agency reported on Wednesday.
The deal was reached during a visit to Tehran on Tuesday by a senior official of Russia's state atomic energy agency Rosatom, IRNA said.
"Iran and Russia reached a preliminary agreement to build at least two new nuclear power plants," Iranian Atomic Energy Organisation spokesman Behrouz Kamalvandi told the news agency.
The two new 1,000 megawatt plants will be built alongside the existing power station in Bushehr, which was also built by Russia, Kamalvandi said.
Further talks will be held on technical and financial aspects of the project but a final agreement is expected to be signed "very soon," he added.
Iran, which still faces tight Western sanctions on its oil and banking sectors despite a landmark agreement reached with major powers in November on its controversial nuclear programme, is expected to fund the project on a barter basis.
Iran's ambassador to Russia, Mehdi Sanaei, said last month that the close trading partners have been negotiating Iran's delivery of hundreds of thousands of barrels of oil per day in return for Russian goods and services, including the planned new nuclear plants.
Russian officials have neither confirmed nor denied the discussions, while stressing that they would not break UN sanctions.
But the White House has raised "serious concern" about the potential of the mooted deal to undermine EU and US sanctions which it credits with bringing Iran to the nuclear negotiating table.
Iran and the powers are still in talks on a long-term agreement to allay Western concerns about its nuclear ambitions.