Dmitry Medvedev, the Russian president, has arrived in New Delhi for talks on joint defence and civil nuclear projects.
The two countries signed an agreement on Friday allowing Russia to build four nuclear reactors in southern India.
Both are expected to approve other defence deals during the Russian leader's three-day visit.
Before arriving in New Delhi, Medvedev said that Russia might also lease nuclear-powered submarines to India as part of a drive to deepen defence ties.
The deal comes after India signed earlier this year a nuclear pact with the US, giving New Delhi access to civilian nuclear fuel and technology on the international market for the first time in three decades.
Overturning a US ban on nuclear trade instituted after India first tested an atomic device in 1974, the US pact provides India with access to nuclear fuel, reactors and technology to generate power for its 1.1bn plus people.
Medvedev was greeted on Friday by Shivshankar Menon, the Indian foreign secretary, and a junior foreign minister, Anand Sharma, before meeting Manmohan Singh, the prime minister.
Russia, now one of the world's biggest arms exporters, has been expanding diplomatic and trade ties with a number of countries.
Moscow recently conducted joint military exercises with Venezuela, a vocal critic of America.
Medvedev also said Moscow would assist India's investigation into last week's Mumbai attacks that killed at least 171 people. He indicated Russia would also be prepared to help on broader issues connected to "fighting terrorism".
The three-day visit is Medvedev's first official trip to India since he took over as president in May this year.