The agreement came at the end of talks between Russian Prime Minister Vladimir Putin and his Indian counterpart, Manmohan Singh, in New Delhi.

"We are building a strategic partnership with India in the nuclear sector," Putin told business leaders in a video conference earlier.

No exact figures on construction of nuclear reactors were immediately available but last December Russia's nuclear energy chief, Sergei Kiriyenko, had said Moscow would build up to 20 reactors at three sites in India.

Singh said the two sides had completed several important defense co-operation projects, emphasizing that ties between the cold war allies remained close. "We regard Russia as a trusted and reliable strategic partner," he said.