The civilian nuclear cooperation deal reverses three decades of American policy by allowing the U.S. to send nuclear fuel and technology to India, which has never signed major international nonproliferation accords and has tested atomic weapons in the past.

Since it was first announced in July 2005 it has been praised as a cornerstone of an emerging partnership between India and the United States after decades on opposite sides of the Cold War divide. But it has also drawn criticism in both countries.

In India, many critics simply oppose closer ties with the United States, and some argue the pact undermines the country's cherished nuclear weapons programme.

Prime Minister Manmohan Singh insisted that was not the case in a speech to lawmakers Monday.

"The agreement does not in any way affect India's right to undertake future nuclear tests if it is necessary in India's national interest," he said.

As he spoke, lawmakers from the Hindu nationalist opposition and from communist parties that support Singh but oppose the deal sought to drown out the prime minister, shouting, "cancel the nuclear deal!"

Similar protests by lawmakers earlier in the day had forced the house to adjourn until Singh spoke in the afternoon.

Singh's speech follows the sealing of a technical pact, known as the 1-2-3 agreement, which details how nuclear cooperation between New Delhi and Washington is to work.

India got nearly everything it wanted in the 1-2-3 agreement, including the right to stockpile and reprocess atomic fuel.

The deal also does not contain a test ban, and some clauses have been interpreted to mean that an Indian test would not automatically scuttle the deal if the move followed tests by either Pakistan or China, India's major rivals.

But the US Congress last year included a test ban when it created an exception for India to American laws that prohibit civilian nuclear cooperation with countries that have not signed the Nuclear Nonproliferation Treaty.