The agreement, which also brings in India, China, Japan and South Korea, was negotiated in secret over the past year and unveiled today on the sidelines of an Asia-Pacific security forum in Laos. Environmental groups immediately expressed concern that it was a device created solely to skewer future negotations on the limiting or reducing global greenhouse gas emissions.

But while Britain formally welcomed the pact, the Government's Chief Scientist, Sir David King, admitted that he had known nothing about it even though climate change was a key item on the agenda of the recent G8 summit at Gleneagles where Tony Blair attempted to win a new consensus on the need for action.

"They seem to have been caught unawares," said Catherine Pearce, International Climates Campaigner at Friends of the Earth. "It's astounding that these discussions were going on in private. To be honest, I find it very suspicious."

The proposed Asia-Pacific Partnership on Clean Development and Climatecreates a framework under which the six leading economic powers in the region powers can collaborate on the development, deployment and transfer of a long list of energy-efficient technologies including carbon capture and storage, methane capture, or nuclear power. It involves no reduction in the use of carbon fuels.

The Government gave the initiative a decidedly cautious welcome. Elliot Morley, the Environment Minister, told the BBC Radio 4 Today programme: "The fact that people are working together, which is very much in line with the agreement at Gleneagles in relation to the action plan on sharing technologies and looking at issues like carbon capture, I think that is a welcome step forward."

But environmentalists, while broadly supporting its aims, fear that the partnership could be used as a means to avoid future commitments under the 140-nation Kyoto protocol or its successor agreements. One described it as a "Machiavellian pact" between the US, eager to protect its technology industry, and Australia's powerful coal producers.

The US, the world's largest polluter, and Australia, which emits the most greenhouse gases per capita, are the only two major developed countries not to have signed up to the 1997 protocol, which demands that greenhouse emissions be cut by 5.2 per cent on 1990 levels by 2012. One of the main objections both nations have deployed is that Kyoto does not impose any targets on fast-growing developing nations.

The next negotiating round to set a regime for the years after 2012 starts in December in Montreal and the idea is for that process to lead to firm commitments on carbon emissions from developing nations.

Robert Zoellick, the US Deputy Secretary of State, told a press conference in Vientiane, the Laotian capital, that the partnership agreement was designed to complement Kyoto rather than replace it. "Our goal is to complement other treaties with practical solutions to problems," he said.

Alexander Downer, the Austraian Foreign Minister, added: "In the end the key to solving these problems is going to be technology ... cleaner technologies, making technologies more economic."

But Ms Pearce said: "What we need to see are targets and timetables and real commitments and nothing I can see so far suggests any targets. This is very much the game plan of the White House - business as usual."

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