President George W. Bush on Monday signed an agreement to allow civil nuclear co-operation with India for the first time in three decades, calling it a “foundation for a new strategic partnership”.

But India’s prime minister warned he would not accept some of the conditions imposed on the deal by the US Congress. In a speech to the Indian parliament, Manmohan Singh said India would not accept “extraneous” conditions.

“India will find it difficult to and cannot accept any such conditions beyond those already agreed to in the understandings with the United States,” he said, warning that “difficult negotiations lie ahead” as the two countries finalised the details of the bilateral agreement. Mr Bush emphasised the benefits of the deal for global energy usage, by helping India move towards cleaner nuclear technology, and the economic benefits of closer ties with India. But Nick Burns, undersecretary for political affairs, adopted more ambitious rhetoric.

He hailed the agreement as helping to “alter the strategic advantage in Asia and south Asia to the benefit of the US”, and called India the “ultimate unfulfilled relationship since partition in 1947”.

Mr Burns sought to play down Indian fears about the new conditions, such as requiring the US administration to report annually to Congress on India’s ties with Iran’s nuclear programme.

He said he met 25 members of the Indian parliament to address concerns, and called the provision on Iran non-binding. “We had to explain to the Indians that, when Congress writes a bill, there are operative paragraphs and there are non-operative, non-binding provisions of any bill . . . ” 

US officials hope the agreement will give US companies such as Westinghouse a “leg up” in contracts for civilian nuclear plants in India, but that cannot proceed until the final bilateral agreement is struck with the US on the details, India signs a safeguards agreement with the International Atomic Energy Agency, and the Nuclear Suppliers Group of 45 civil nuclear countries lifts its restrictions on India.

“How long will this take if we are in fifth gear? I would hope it could take six months,” said Mr Burns.

He was confident that NSG approval would be given.