Rich nations that pledged to reduce greenhouse gases under the Kyoto Protocol agreed Wednesday night at UN climate talks here to extend these obligations, but failed to cite hard numbers, oberservers here said.

The 37 so-called Annex 1 industrialised countries "agreed that further commitments ... under the Kyoto Protocol should, for the next commitment period, principally take the form of quantified emission limitation and reduction objectives," said the draft text.

Absent from the document, hammered out in a tense working group, is any direct mention of the target range for cuts in carbon pollution.

Russia, Canada, Japan and Australia in particular replaced numbers included in an earlier draft with a reference to the December 2007 "Bali Roadmap", in which the world's nations gave themselves two years to reach a global climate deal, observers said.

They also lobbied to include the word "principally", leaving open the possibility that commitments could take other forms besides measurable reductions in CO2 output.

The Roadmap does not specify any clear emissions goal, nor does it suggest which countries should make emissions cuts or how deep these cuts should be.

But in a footnote in the preamble, it refers to scenarios by the UN's Nobel-winning scientists, the Intergovernmental Panel on Climate Change (IPCC), which include a goal of halving global emissions by 2050, compared with the level for 2000.

Rich countries would have to cut their emissions by 25-40 percent by 2020.

The new draft document could come before a plenary session Thursday at the UN Framework Conference on Climate Change (UNFCCC), the international body charged with forging a deal that will take over when Kyoto's provisions expire in 2012.

Green groups said the new wording of this core commitment was "a step backwards."

"We have had no forward movement in a year, and we find ourselves exactly where we were in Bali," said Damien Demailly, coordinator for climate at WWF France.

"China, it should be noted, saw this as an attempt to find an escape hatch" from firm national pledges to reduce greenhouse gases, he said.

The first commitment period under Kyoto, from 2008 through 2012, calls on highly industrialised countries to trim their emissions by five percent compared to 1990 levels.

Many countries will not be able to keep even these commitments, scientists say.

The December 1-12 conference in the Polish city of Poznan, gathering more than 11,600 participants from around the world, steps up a gear on Thursday with the start of two days of ministerial-level talks.