Russia is already building two reactors in the southern Indian state of Tamil Nadu.

"The agreement sees construction of up to 16 nuclear reactors in three locations," Deputy Prime Minister Sergei Ivanov, accompanying Mr Putin, said.

Russia is competing with French and US firms for contracts to build nuclear power plants in Asias third-largest economy which is looking to increase its energy supply to sustain rapid economic growth.

The increased competition began after Indias landmark civilian nuclear deal with the US in 2005 which ended the isolation India had experienced since it tested an atom bomb in 1974.

"This is one of our most important and promising areas of co-operation," Mr Putin said in New Delhi on Friday.

Coal still accounts for more than 50% of Indias energy use - but a substantial expansion of nuclear power reactors is proposed over the next few decades.

Fighter aircraft

Over the next decade alone, the contribution of nuclear energy is expected to rise from just 3% to 6% of Indias total needs.

The two countries have had close links since Soviet times, with India remaining a top buyer of Russian weaponry.

However, the relationship faces new challenges, including competition from the West and the growing economic and military might of China.

As part of the deals signed during Mr Putins visit, Russia will refit an aircraft carrier, supply an additional 29 fighter aircraft to India and jointly develop transport aircraft.

Russian and Indian officials also discussed boosting bilateral trade, which is currently worth $8bn.