Environmentalists have reacted with anger to a decision by US President George W Bush not to reduce carbon dioxide emissions from power stations.
A spokesman for the Sierra Club lobby group, Dan Becker, accused Mr Bush of turning his back on the most important environmental problem facing the country.
An official from Japan's Environment Ministry was quoted as saying that the decision, if confirmed, was regrettable and could undermine the 1997 Kyoto protocol aimed at reducing greenhouse gases.
He's ended the shortest honeymoon in history
Sierra Club spokesman
Mr Bush said in a letter to Republican Senator Chuck Hagel that the decision was prompted by fears of aggravating the energy crisis faced in particular by the far West of the United States.
Mr Bush originally pledged the reduction during last year's presidential election campaign.
He is now seeking justification for his change of policy on technical grounds, noting that the 1970 Clean Air Act does not class carbon dioxide as a pollutant.
The letter says that three other substances included in the original strategy - nitrogen oxide, sulphur dioxide and mercury - will be controlled as part of a balanced policy.
Mr Becker told the BBC that the president had reneged on a pledge he had made to fend off criticism of his environmental record in Texas.
"He has betrayed a campaign promise, he's turned his back on the entreaties of world leaders... and he's ended the shortest honeymoon in history," he said.
He described as a "red herring" the Clean Air Act's failure to mention carbon dioxide, saying that powerful industrial lobbies had prevented any new consideration of global warming within it.
The main body of scientific opinion now recognised the gas as a major contributor to global warming, he added.
The change of position has resulted from a review of policy led by Vice President Dick Cheney.
The "four pollutant strategy", announced in September, was one of Mr Bush's few specific proposals on climate change.
Christie Whitman, the head of the Environmental Protection Agency, recently reasserted the pledge at a meeting with environmental ministers from major industrial countries in Italy.
But her remarks prompted a lobbying campaign by coal and utility companies, some of whom are strongly opposed to mandatory controls on carbon dioxide.
Mr Bush's letter was released on the same day that the Department of Energy announced its participation in a new institute in the state of Washington to study global warming.