China's top newspaper called a nuclear agreement between India and the United States a "major blow" to non-proliferation, raising pressure as the deal faces opposition in an international atomic cartel.
The commentary on Monday in the People's Daily, the ruling Chinese Communist Party's official paper, was a rare public response from Beijing on the controversial US proposal to lift a ban on nuclear trade with India.
Diplomats in Vienna said on Sunday that a revised US proposal to lift the ban did not sufficiently ease fears the move could compromise efforts to stop the spread of nuclear weapons.
Washington needs an unprecedented exemption from the Nuclear Suppiers Group's normal rules to help seal its 2005 civilian nuclear energy deal with New Delhi. But at the group's meeting, six member nations demanded changes to ensure Indian access to nuclear markets would not indirectly help its atomic bomb programme.
Chinese officials have remained tight-lipped about the deal and given no sign they would outright block it, but official media and experts have raised worries.
The Party's official paper was unusually forthright on Monday.
"Whether it is motivated by geopolitical considerations or commercial interests, the US-India nuclear agreement has constituted a major blow to the international non-proliferation regime," said the commentary by a researcher from the Chinese Academy of Social Sciences, a leading state think tank.
"Irrespective of the fate of the US-India nuclear agreement, the United States' multiple standards on non-proliferation issues have met with a sceptical world."
Without NSG approval in early September, the US Congress may run out of time for final ratification before it adjourns at the end of the month for autumn elections.
The deal is controversial since India has shunned the Non-Proliferation Treaty, which commits members to nuclear disarmament, after developing atom bombs with Western technology imported ostensibly for peaceful nuclear energy.
Experts have said China is unlikely to stymie the nuclear deal and risk pushing Delhi closer to Washington when Beijing is seeking to avoid confrontation with its rising Asian neighbour.
But many have also said that Beijing worries about how the deal will affect regional security and arms controls.
China and India, the world's two most populous nations, are forging new ties amid soaring trade and business links, though serious differences over their Himalayan border, the cause of a 1962 war, fester.
India and rival Pakistan both tested nuclear devices in 1998, raising tensions between the neighbours. Pakistan is a close partner of China.
China was not among the six nations that raised objections in the NSG meeting, but the commentary was a reminder that Beijing was irked by the nuclear agreement.
The United States' initial proposal to the NSG was "vague" and "left the concerned papers very dissatisfied", the newspaper said.
"As there is no constraining link between supply of nuclear materials and India conducting a nuclear test," it added. "India need not assume strict non-proliferation responsibilities."