The US has dismissed a suggestion from UK Prime Minister Tony Blair that it may be prepared to sign up to binding targets to tackle climate change.
The US believes binding targets would damaging economically
Speaking at UN climate talks in Canada, the US chief negotiator said his nation would not enter talks about fixed curbs on emissions of greenhouse gases.
Mr Blair told UK business leaders on Tuesday that he believed all major nations would support new targets.
The current targets within the Kyoto Protocol will expire in 2012.
"We would certainly not agree to the United States being part of legally binding targets and timetable agreement post-2012," Dr Harlan Watson, the head of the US delegation, told reporters at the climate conference in Montreal.
Dr Watson was responding directly to comments made by the UK prime minister at a Confederation of British Industry conference in London.
Mr Blair told delegates: "Climate change is producing a sense of urgency. I have no doubt where policy is heading, here, in the US, [and] across the emerging economies of the world.
"I believe there will be a binding international agreement to succeed Kyoto when the protocol expires in 2012 that will include all major economies."
Environmental groups at the UN gathering say Mr Blair is suffering from wishful thinking if he believes there will be any substantial movement from the US from its existing policy.
Thousands of participants in Montreal are pondering how to meet the targets in the Kyoto treaty, and what measures should follow when these expire in 2012.
The host nation wants to find a formula to include dissenting countries and developing states not covered by Kyoto.
The Kyoto accord came into force earlier this year, seven years after it was signed back in 1997. It requires industrialised nations to cut their emissions of CO2 (carbon dioxide) and other gases blamed for warming the planet.
Some 156 countries have ratified the treaty, which pledges to reduce global emissions by 5.2% by 2012.
But the US - the world's top emitter - has not signed up, saying it is too costly to introduce and that the agreement is flawed.