Legislation sailed through Congress early on Saturday, ending the isolation imposed after New Delhi developed nuclear weapons in contravention of international standards.

The deal, first agreed in July 2005, has caught the imagination of many in India and is seen as a major move toward becoming a regional power. But it has also attracted criticism after it was modified in the US legislature.

In a sign of the battle the government faces, the Bharatiya Janata Party, which ruled the country between 1998 and 2004, said early fears the United States was only interested in capping India's nuclear weapons program "stood confirmed."

A BJP statement said the bill did not deliver full civil nuclear cooperation, imposed "rigorous" assessment obligations, failed to guarantee uninterrupted fuel supplies for civilian reactors and prevented India from reprocessing spent fuel.

It also banned future nuclear tests and rendered the weapons programme "subject to intrusive US scrutiny."

Strategic analysts and members of the Indian nuclear establishment have cited similar concerns.

They argued against inspections and said the deal would constrain India's military nuclear programme by separating it from the civilian side.

An earlier draft stated that cooperation would depend on India's support for international efforts to restrain Iran's nuclear programme, rankling New Delhi.