The UN climate chief warned Monday that time was running out to break a deadlock on a global warming pact, telling delegates in Bangkok that failure to do so by December would threaten future generations.

The talks are the next to last before a showdown in Copenhagen at the end of the year, when the 192 countries must agree on a treaty for tackling greenhouse gases beyond 2010, after the current Kyoto Protocol expires.

"Time is not just pressing, it has almost run out," said UN climate head Yvo de Boer, who broke down in tears of frustration at talks in Bali two years ago, when world governments drew up the "road map" to the Copenhagen deadline.

After two years of haggling, the world is still trying to thrash out a draft text for December's talks, with major disagreements on the two key issues of cutting carbon emissions and meeting the associated costs.

"There is no plan B, and if we do not realise plan A the future will hold us to account for it," de Boer said in his opening speech to around 2,500 government delegates and representatives from business and environment groups.

De Boer said that devastating floods in the Philippines at the weekend which have killed at least 140 people further highlighted the need for action.

"One of the reasons why countries have gathered here is to ensure the frequency and severity of those kinds of extreme weather events decreases as a result of ambitious climate change policy," de Boer said.

The Bangkok talks, part of the UN Framework Convention on Climate Change (UNFCCC), run until October 9. The final talks before Copenhagen are in Barcelona from November 2-6.

The meeting in the Thai capital follows last week's UN climate summit in New York and a G20 meeting in Pittsburgh, both of which failed to break the deadlock on either of the two biggest issues.

"Our children and grandchildren will never forgive us unless action is taken. Time is running out, we have two months before Copenhagen," Thai Prime Minister Abhisit Vejjajiva said in his opening speech on Monday.

De Boer said on the eve of the Bangkok talks that they had a 280-page negotiating text which is "basically impossible to work with."

The US on Monday reaffirmed its commitment to signing the treaty.

"We want to be part of a new agreement," said Jonathan Pershing, the US head of delegation in Bangkok.

The US -- which signed the Kyoto deal but later saw it rejected by Congress -- is due to introduce its new climate change and energy bill in the Senate this week and there are fears the bill will not pass ahead of Copenhagen.

Pershing said the United States was "working quite aggressively trying to promote action in the Congress."

While the European Union, pegged to a 1990 benchmark, has set a 20 percent target for emissions cuts by 2020, and Japan 25 percent if others follow suit, the US so far has only set the equivalent of four percent as a target.

Experts warn that global temperatures must rise no more than two degrees Celsius (3.6 degrees Fahrenheit) by 2100 over pre-industrial times, a target embraced by the leaders of the G8 nations in July.

Scientists also say emissions of heat-trapping greenhouse gases should peak just six years from now.

Without drastic action they fear drought, floods and rising sea levels could grip the world by the end of the century causing famine, homelessness and strife.

On emissions, developed economies including the US have acknowledged a historical responsibility for global warming. Most have put numbers on the table for slashing their carbon pollution by 2020 and by 2050.

But they say that developing nations -- especially China, India and Brazil and other major emitters of tomorrow -- should also pledge to curb output of greenhouse gases.

Poor and emerging economies refuse to take on their own hard targets but call for rich nations to make higher cuts.