The pact, signed on Friday in Tokyo by Japanese Prime Minister Shinzo Abe and his Indian counterpart Narendra Modi , marked the first time Japan agreed to such a deal with a country that is not a member of the Nuclear Non-Proliferation Treaty.

Critics in Japan, the victim of US atomic bombings in the final days of World War II, have previously raised concerns about a risk of the country's technology being diverted to India's nuclear weapons programme.

Yet, the deal is limited to peaceful commercial use, and Tokyo cam terminate it if India conducts a nuclear test.

The pact allows India to reprocess fuel and enrich uranium, though highly enriched uranium that can be used to make nuclear weapons is not permitted without written agreement by Japan.

India's Nuclear Riddle - People & Power
Abe and Modi insisted the agreement will contribute to peaceful use of clean energy.

"This agreement sets a legal framework to assure that India acts responsibly for the peaceful uses of nuclear energy," Abe said, adding that it gets India to effectively participate in the non-proliferation treaty framework.

"It is also in line with Japan's position to promote non-proliferation to create a world without nuclear weapons."

Abe's pro-business government seeks to export nuclear power plants to counter shrinking sales at home since the 2011 Fukushima nuclear disaster, and has discussed similar deals with Vietnam and Turkey.

Modi praised the signing as "a historic step in our engagement to build a clean energy partnership" that will help India to "combat the challenge of climate change".

Anti-nuclear groups denounced the agreement, citing threats to safety and regional peace and increased risk of proliferation.

"There is no effective separation between India’s nuclear energy programme and its weapons programme, and the Japanese government’s agreement conditions are meaningless," Shaun Burnie, a senior nuclear specialist at Greenpeace Japan, said in a statement .

"Approving nuclear trade with India is a geo-strategic decision to support further nuclear weapons proliferation in Asia."

The women of Fukushima, an anti-nuclear lobbying group, have issued an appeal to Modi to visit the disaster area and see at first hand the consequences of nuclear power.

"Nuclear power plants will not bring happiness to your citizens," the group said in an open letter.

"We who experienced the injury of the nuclear accident, we came to understand this through our own bodies and lives."

Energy-hungry India wants to increase nuclear power generation to support its strong economic growth. The country has signed similar nuclear agreements with France, Russia, Britain and the United States.