Russia will begin building two nuclear reactors in Iran next week, a top Iranian atomic energy official has said.
The news comes a year after Tehran signed a contract with Moscow to construct a further two reactors at the existing Russian-built Bushehr power plant in southern Iran.
Behrouz Kamalvandi, deputy head of the Atomic Energy Organisation of Iran, said work on the two reactors "will commence next week", according to the state television website.
A series of agreements signed between the two countries last year foresees eventually increasing the total number of Russian-built reactors in Iran to nine.
Construction of the two reactors will be bankrolled by Iran, Sergei Kiriyenko, head of Russia's state nuclear company Rosatom, said last year.
The start of the work follows a landmark deal between Iran and world powers in July that ends a decade-long standoff over Tehran's nuclear programme.
The accord does not limit Iran's development of civilian nuclear sites.
Meanwhile, Denis Manturov, Russia's industry and trade minister, said on Tuesday that Moscow was considering lending $5bn to Iran next year.
"We're talking about providing a state credit, under the guarantee of the Iranian government," Manturov said, according to the state news agency RIA Novosti.
Preliminary documents for lending the sum to Iran via an intergovernmental export credit were signed during Russian President Vladimir Putin's visit to Tehran in late November.
The two countries have recently allied to prop up Syrian President Bashar al-Assad against opposition and armed groups.