The head of the United Nations nuclear watchdog has welcomed a nuclear agreement between the US and India.
International Atomic Energy Agency chief (IAEA) Mohammed ElBaradei said it would boost non-proliferation efforts.
The UK and France also hailed the deal. But it was criticised by some members of the US Congress, who said it would lead to the spread of nuclear weapons.
Under the accord, India gets access to US civil nuclear technology and opens its nuclear facilities to inspection.
US President George W Bush - who finalised the agreement with Indian Prime Minister Manmohan Singh in Delhi - called it "historic".
However, Mr Bush admitted it might be hard to get it through the US Congress, which must ratify it.
The BBC's Jonathan Beale in Washington says Mr Bush has a fight on his hands, after being accused of sending out the wrong signal just as America and its allies try to limit Iran's nuclear ambitions.
India has not signed the Nuclear Non-Proliferation Treaty (NPT).
Under the agreement, India will classify 14 of its 22 nuclear facilities as being for civilian use, and thus open to inspection.
Many supporters of the NPT believe the deal ignores India's nuclear weapons programme.
Mr ElBaradei said the US-Indian deal would end Delhi's nuclear isolation and spur non-proliferation efforts.
"It would be a milestone, timely for ongoing efforts to consolidate the non-proliferation regime, combat nuclear terrorism and strengthen nuclear safety," he said.
Mr ElBaradei also said the agreement was "an important step towards satisfying India's growing need for energy".
UK Prime Minister Tony Blair said the accord could "make a significant contribution to energy security... as well as representing a net gain for the non-proliferation regime".
French President Jacques Chirac, who signed a similar deal with India last month, said the agreement would help fight climate change and non-proliferation efforts.
However there was a mixed reaction in Washington.
Some congressmen cautiously welcomed the agreement, despite the lack of details.
NUCLEAR POWER IN INDIA
India has 14 reactors in commercial operation and nine under construction
Nuclear power supplies about 3% of India's electricity
By 2050, nuclear power is expected to provide 25% of the country's electricity
India has limited coal and uranium reserves
Its huge thorium reserves - about 25% of the world's total - are expected to fuel its nuclear power programme long-term
Source: Uranium Information Center
Ed Royce, Republican chairman of the House subcommittee on terrorism non-proliferation, said there was enthusiastic support for improving ties with India.
However, he added that the deal had wider implications that Congress would have to consider carefully.
Ed Markey, senior House Democrat, said the agreement was a "historic nuclear failure" that compromised American security.
"The president has blown a hole in the nuclear rules the whole world has been playing by," Mr Markey said.
Pakistan - India's regional rival - said it would be pressing the US to give Islamabad the same kind of civilian nuclear co-operation.
"We also have a claim... especially because Pakistan is a fossil fuel-deficit country," Pakistani foreign ministry spokeswoman Tasnim Aslam told the BBC.
However, US Secretary of State Condoleezza Rice told India's Zee News that "this is not the time for such an arrangement with Pakistan".
"There have been concerns in terms of proliferation with Pakistan," she said in an apparent reference to a row over Pakistan's top nuclear scientist Abdul Qadeer Khan, who admitted to leaking secrets to North Korea, Libya and Iran.