The chief American negotiator at the conference in Argentina's capital Buenos Aires ruled out any move to sign up to the Kyoto Protocol for years.

Dr Harlan Watson said efforts to cut emissions were based on bad science.

The US was focused instead, he said, on implementing President George W Bush's plans to promote energy efficiency.

At the beginning of this year's conference on global warming, the head of the Climate Change Convention had seemed to be offering an opening to the US.

Olive branch

It was suggested that in the next phase of action after 2012, countries might be able to pursue different routes towards a similar end.

The US mantra has been that it is committed to addressing climate change but has simply chosen a different path.

But if it was an olive branch, the US has brushed it aside.

Dr Watson, who is leading the American delegation here, told a news conference that this was not the moment for the US to reassess its policies.

Scathing judgement

He said US President George W Bush had a 10-year programme to reduce the carbon intensity of the US economy by 18% by 2012.

The government was totally committed to carrying out the programme and wanted to wait to see the results, he added.

But Dr Watson admitted that even if the US achieved its target, it would still be producing 15-16% more greenhouse gases while the rest of the industrialised world was committed to an absolute reduction.

He was scathing about the way the rest of the world was approaching climate change, arguing that the Kyoto Protocol was a political document and not based on sound science.

Dr Watson said the protocol was more about being seen to agree than about actual action.

He challenged any of the Kyoto parties to match the US in the practical steps it was undertaking.