BANGKOK (AFP) – UN climate talks in Bangkok are the most constructive since the 2007 launch of negotiations to deliver a planet-saving pact on global warming, the UN climate chief told AFP on Wednesday.

"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.