Tired delegates voiced their fury, thinly veiled in diplomatic language, after Russia held up an agreement to launch negotiations on the next round of pollution-cutting pledges under the UN's Kyoto Protocol.

The marathon conference of the UN Framework Convention on Climate Change (UNFCCC) was to have ended late Friday, but hardline tactics by the United States and then Russia caused the backroom haggling to go into overtime.

Asked by AFP whether an overall deal could be reached in Montreal, British Environment Secretary Margaret Beckett said: "I don't know. It's entirely possible -- all the ingredients are there."

Jennifer Morgan, a campaigner with the green group WWF, was more optimistic, predicting: "It's going to happen."

Early Saturday, United States, pressured from all sides, was willing to lift its opposition to a "dialogue" on how the UNFCCC can enact deeper cuts in greenhouse gas pollution, sources said.

The proposal put forward by conference host Canada is for a "dialogue on long-term cooperative action" on cuts in greenhouse gases that makes no mention of any goals or measures to be taken.

It draws on text that the United States has already approved in other fora, including the Group of Eight (G8) summit in Gleneagles, Scotland, in July.

Washington on Wednesday warned it opposed any move that would drag it into "formalised discussions" and away from its purely voluntary approach to tackling emissions.

The sources said the US delegation was willing to lift its objections in exchange for scaling back the scope of the "dialogue," notably by dropping two proposed meetings out of a maximum of four.

The draft text still has to be approved by a plenary of the UNFCCC conference.

Bringing the United States back into the multilateral fold is seen as essential for combatting global warming.

The United States is the world's top polluter, accounting by itself for nearly a quarter of all greenhouse gas emissions.

But in 2001 it walked away from the Kyoto Protocol, citing the cost of meeting its binding targets for reducing the pollution.

The Montreal conference was also tasked with advancing the objectives of the Kyoto Protocol itself.

By late Friday, Kyoto members had reached deals on a range of important questions, including the treaty's policing mechanisms.

But agreement for launching negotiations on cuts that should be made after the accord's present pledging period runs out in 2012 was suddenly delayed in the pre-dawn hours of Saturday by Russia.

It demanded in essence that the future negotiations allow developing countries which make "voluntary" cuts in their emissions to enjoy the same market incentives mechanisms as industrialised countries under the Protocol.

Delegates from other Kyoto countries objected to this.

Some pointed out that the Russian demand amounted to a virtual rewrite of a rulebook that took four years to negotiate.

Others said that a failure in Montreal would cast a dark shadow over the fledgling carbon market, which needs a signal that it will operate beyond 2012.

Greenhouse gases are the carbon byproduct of burning oil, gas and coal.

Billions of tonnes are released into the air each year, trapping heat from the Sun and causing what scientists say are early signs of climate change -- disruption of rainfall patterns, melting glaciers and polar sea ice and, possibly, the 2005 Atlantic hurricane season, the worst on record.

Even if all the present Kyoto goals are met, industrialised countries will have trimmed output of greenhouse gases by just one or two percent by 2012 as compared to a 1990 benchmark.

Tackling the problem will thus require a broader, longer-term approach, bringing in the United States as well as possibly Brazil, China and India, and encouraging the switch away from dirty fossil fuels to cleaner energy sources.

That is the biggest challenge of all, because oil, gas and coal have a tight grip on the world's energy market, enjoying a big price advantage and political clout over new, cleaner alternatives such as solar, wind, hydrogen and biofuels.

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