The 190-nation conference reached an agreement in a dramatic 13th, unscheduled day to set a 2009 deadline to draw up a landmark pact, after the US backed down on last-ditch objections.

After all-night talks, the Bali conference agreed to launch a two-year round of talks for the most ambitious treaty ever attempted for reining in greenhouse gases.

But under US pressure, the deal dodged the goal of halving these emissions by 2050 or of embracing a commitment by industrialized economies to slash their own emissions by 2020 to help set the horse-trading in motion.

Both had been set down by the EU and supported by developing countries as a prerequisite for negotiations that would be bold and put the whip to rich countries historically to blame for global warming.

The agreement came only after the head of the UN jetted in and the UN climate chief nearly broke down in tears.

UN Secretary-General Ban Ki-moon flew in to make an unscheduled last-minute appeal for a deal.

The US reached a compromise with the EU on Friday to avoid specifying a target for slashing greenhouse gas emissions.

But yesterday, the US backed down from the agreement, saying it would not accept an accord because it wanted developing countries such as China to make tougher commitments.

Senior US negotiator Paula Dobriansky told the conference that the US would reject the draft.

Dobriansky was loudly booed by other delegations. A US delegate representing Papua New Guinea said on the floor to rousing cheers: "If you're not willing to lead, please get out of the way."

After repeated verbal lashings, Dobriansky again took the microphone and said Washington would "go forward and join consensus," to the cheers of the conference.

After the accord, environmental groups accused the US of gutting a pact that would have ensured those talks got off to a flying start.

"What you've got is a situation where the overwhelming majority of countries are progressive, they're pushing for a deal, and the [US] administration was out on a wrecking mission," said Hans Verolme of the World Wildlife Fund.

"Yes, we're launching negotiations," he said. "What they don't have is a clear reference to the best available science that should inform these negotiations."

He and other activists said, however, that the process launched in Bali would ensure a seat at the next table for US President George W. Bush's successor.

"The Americans have actually climbed down on things that 12 months ago they fundamentally rejected," said Steve Sawyer, secretary general of the Global Wind Energy Council.