"This is the first time over the past two years that we have seen this kind of constructive focus on how we are actually going to make this thing work," said Yvo de Boer, executive secretary of the UN Framework Convention on Climate Change (UNFCCC).

"We are now in the eye of the storm... The bricks and mortar of a Copenhagen agreement are being worked on here," he said in an interview in the Thai capital.

"I hope we can sustain that," he added.

Delegates from 180 countries have been locked in the talks for 10 days, trying to lay the groundwork for a global deal to be hammered out during a December conference in Copenhagen.

The new agreement would supersede the Kyoto Protocol, whose provisions expire in 2012.

Negotiations over the past two years have remained largely deadlocked, with rich and poor nations disagreeing on how to share the burden of slashing heat-trapping greenhouse gases and how to pay for it.

"There is the beginning of a constructive discussion on finance," suggested de Boer.

He said, however, that rich economies are unlikely to say before December how much money they will provide to developing nations to fight global warming and cope with its consequences.

The UNFCCC estimates that the figure needed could run into several hundred million dollars a year by 2020.

Where progress has been made is on the critical issue of how those funds will be distributed, de Boer said.

Industrialised countries favour using existing institutions such as the World Bank, while poorer nations want to set up a special UN-run fund.

There is also movement, he said, on another hot-button issue: the fate of the Kyoto Protocol, the only international treaty on curbing the output of greenhouse gases.

Under its provisions, 37 industrialised countries have made national commitments to reduce their carbon pollution by a certain amount, measured against a 1990 benchmark. Among rich countries, only the US opted out.

Up to now, developing countries -- with emerging giants China and India at the lead -- have said Kyoto must be renewed and strengthened, while rich nations, led by the US, prefer folding some of its provisions into a new deal.

"There is a willingness now to talk about -- at least in theory -- what would happen to all the good things under Kyoto if it were not to continue," said de Boer.

"Can you strip out some of the Kyoto bits and put them into a new agreement?" he added.

De Boer cautioned that the thawing of positions in Bangkok was only a small part of what was needed for a successful agreement in Copenhagen.

"At the end of the day, if you don't have ambitious (emissions reductions) targets from rich nations, and if you don't have significant finance on the table, the whole thing falls apart," he said.

"Without that, we are having a very constructive discussion here for nothing."

The developing world has called on industrialised countries to commit to 40 or 45 percent cuts in emissions by 2020, compared to the 1990 benchmark.

The European Union has pledged to cut its carbon dioxide pollution by 20 percent, and Japan by 25 percent if other countries follow suit.

In the US, legislation wending its way through Congress would cut carbon output by the equivalent of about four percent from the 1990 mark.

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