The 45-member NSG gathered at the headquarters of Japan's permanent mission to the IAEA in Vienna to debate a proposal by the United States for a special NSG waiver for India, which currently cannot receive foreign nuclear materials and technology as it has not signed the Nuclear Non-Proliferation Treaty (NPT).

The NSG's rules usually ban trade with states that have not signed the NPT.

The proposed US-India nuclear cooperation deal has already been given the green light by the UN atomic watchdog when the International Atomic Energy Agency approved a special safeguards agreement with India.

But it must now also clear the NSG hurdle before it can finally be voted on by the US Congress.

Critics have said the deal undermines international non-proliferation efforts by providing US nuclear technology to a non-NPT state that developed atomic bombs in secret and conducted its first nuclear test in 1974.

Diplomats said the NSG was not expected to make a final decision this week and another meeting in early September could be necessary to reach consensus.

Diplomats said that a number of countries including Austria, Ireland, the Netherlands, New Zealand, Switzerland and Scandinavian countries would propose amendments to the US draft deal.