India and Russia today signed a nuclear co-operation agreement, which paves the way for the building of about a dozen nuclear reactors in India, with Russian help, over the next few decades.

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 defence co-operation projects, emphasising that ties between the cold war allies remained close. "We regard Russia as a trusted and reliable strategic partner," he said.

The two countries signed a $1.5bn (£1bn) deal for Russia to sell MiG-29K aircraft carrier-based fighter jets to India, with the first deliveries to begin in 2012. The leaders also agreed to intensify their consultations on Afghanistan in tackling the challenges posed by terrorism and extremism in the region, Singh said.

Earlier, Putin told the business leaders that the activities of extremist groups in Afghanistan and Pakistan were a "matter of worry for the entire region and the whole world". "Parts of Afghanistan's soil continue to be used by terror groups. We understand the concerns of India regarding the activities of banned outfits in Pakistan," he said.

Other agreements signed Friday included one on the production of satellite navigation systems and others relating to hydrocarbons and the energy sectors, officials said.

Putin also held talks today with India's President Pratibha Patil and ruling Congress party leader Sonia Gandhi.

Discussions between Putin and Singh focussed on strengthening the decades-old bilateral ties between the two countries and examined ways to take them forward as India's burgeoning economy is courted by other players.

India remains one of the world's biggest arms importers and a top Russian arms client, with Moscow supplying nearly 70% of New Delhi's military hardware. Putin said Russia was pursuing technical military co-operation with India that included joint work on a next-generation fighter jet. The two sides further signed a series of agreements marking the end of a protracted dispute over the cost of refurbishing a Soviet-built aircraft carrier, the Admiral Gorshkov, for the Indian navy.