Yvo de Boer, head of the UN Convention on Climate Change which is chairing talks in Bangkok, said the highly sensitive issue should be thrashed out next year, after the US elections in November.

"There are some topics which it makes sense to leave for later in the process, for example what sort of targets or commitments are industrialised countries going to agree to," he told reporters.

"That is something which is perhaps more sensibly discussed with a new administration."

Under President George W. Bush, who will leave office in January, the United States backed out of the Kyoto Protocol, the landmark pact on cutting emissions whose obligations expire at the end of 2012.

Bush argued that the treaty was unfair by making no demands of developing countries. But the three major candidates vying to replace him have all pledged tougher action on global warming.

Frustration with the current US stance grew so great during landmark talks in Bali, Indonesia, in December last year that American delegates were booed during the conference's closing hours.

All participants eventually agreed to reach a new pact on post-Kyoto commitments by the end of 2009.

But the Bali Road Map contained no explicit mention of emissions cuts for rich countries.

The United States is pushing for fast-developing nations such as India, China and Brazil to sign up to binding carbon emissions cuts, while Europe is leading calls for rich countries to slash emissions by 25 to 40 percent by 2020.

De Boer said US participation had so far been positive at the Bangkok talks, which aim to lay out an action plan for negotiations toward next year's pact on halting the ravages of climate change.

"The US is very much engaged in the process here. That doesn't mean that we immediately have consensus and everybody is ready to sign up to a final deal," he said on the second day of the Bangkok meeting, which ends Friday.

He said the US delegation has been "constructive" in the Bangkok talks, including by putting forward an idea on how to organise key parts of the discussions on reaching a new treaty.

De Boer, who has warned that time is running out to forge a new pact on global warming, said he was encouraged with progress in the Thai capital.

"We could potentially have had a big fight over the agenda, we didn't. We could potentially have had a fight over the fact that very interesting meetings are happening in parallel. We didn't," he said.

"I take from that a sense that countries really want to get down to work, rather than fight procedural wars."

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