Russia's state-owned Rosatom said it would supply 12 nuclear energy reactors for India over 20 years, under an agreement aimed at boosting nuclear energy cooperation signed by the two countries during a summit in New Delhi on Thursday.
A 1,000-megawatt reactor is operating at the Russian-built Kudankulam power station in India's Tamil Nadu district, with a second due to come on stream in 2015.
Russian President Vladimir Putin had been pushing for Rosatom to increase the number of reactors it could supply to as many as 25.
Indian officials say that a total of six reactors will be built at Kudankulam, with a further six to follow at a site that has not yet been determined.