They reached the agreement during bilateral talks in New Delhi on October 4.

India now considers the US as its largest trading and investment partner, said Ms Rice's Indian counterpart Pranab Mukherjee, who also said bilateral ties will grow further as the nuclear deal allows India to build more nuclear reactors to satisfy its surging demand for energy.

The pact offers India access to sophisticated US technology and cheap atomic energy in return for New Delhi allowing UN inspections of some of its civilian nuclear facilities.

The two countries had spent three years negotiating the deal since President George W. Bush and Indian Prime Minister Manmohan Singh first agreed to it in 2005.

Ms Rice and others had to lobby hard to win approval for the deal from the International Atomic Energy Agency (IAEA), the UN nuclear watchdog, and the Nuclear Suppliers Group (NSG), which controls global atomic trade.