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As U.N. talks entered their final hours, European nations on Thursday threatened to boycott a U.S.-led climate meeting next month unless Washington agrees to a deal mentioning numerical targets for deep reductions in global warming gases.

The United Nations warned that time was running out for an agreement aimed at launching negotiations for a successor to the Kyoto Protocol and the talks in Bali were in danger of "falling to pieces."

The United States, Japan, Russia and several other governments refuse to accept language in a draft document suggesting that industrialized nations consider cutting emissions by 25 percent to 40 percent by 2020, saying specific targets would limit the scope of future talks.

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The European Union and others say the figures reflect the measures scientists say are needed to rein in global warming and head off predictions of rising sea levels, worsening floods and droughts, and the extinction of plant and animal species.

"No result in Bali means no Major Economies Meeting," said Sigmar Gabriel, top EU environment official from Germany, referring to a series of separate climate talks initiated by U.S. President George W. Bush in September. "This is the clear position of the EU. I do not know what we should talk about if there is no target."

Brazil's Climate Change Ambassador Sergio Barbosa Serra said his government was not threatening a boycott, but would take any omission of numerical targets "into account" when it decides whether to attend the Major Economies Meeting.

The U.S. invited 16 other major economies to that Washington meeting, including European countries, Japan, China and India, to discuss a program of what are expected to be nationally determined, voluntary cutbacks in greenhouse gas emissions.

The Bush administration views the major economies process as the main vehicle for determining future steps by the U.S. — and, it hopes, by others — to slow emissions.

But environmentalists accuse the U.S. of trying to undermine the U.N. process, which since Kyoto has focused on internationally binding targets. Many delegates here believe no such international action is possible until the Bush administration leaves the White House in January 2009.

The talks bring together nearly 190 governments in Bali are scheduled to wrap up Friday.

But U.N. climate chief Yvo de Boer said he was worried the U.S.-EU deadlock could derail the process and that a final "Bali roadmap" would contain an agreement to negotiate a new climate deal by 2009, but may not include specific targets for emission reductions.

"I'm very concerned about the pace of things," he said. "If we don't get wording on the future, then the whole house of cards falls to pieces."

The United States delegation said while it continues to reject inclusion of specific emission cut targets, it hopes eventually to reach an agreement that is "environmentally effective" and "economically sustainable."

The United States is the world's largest emitter of greenhouse gases and the only major industrial country to have rejected Kyoto, which expires in 2012. It has been on the defensive since the conference kicked off on Dec. 3.

Pressure has come even from a one-time ally on climate, Australia, whose new prime minister urged Washington to "embrace" binding targets, and from former U.S. Vice President Al Gore, who won this year's Nobel Peace Prize for helping alert the world to the danger of climate change.

But U.S. Under Secretary of State Paula Dobriansky, the head of the American delegation, told reporters that the conference was simply the start of negotiations, not the end.

"We don't have to resolve all these issues ... here in Bali," she said.

That did not satisfy environmentalists, who accused Washington of standing in the way of a meaningful deal — and not just on the inclusion of emissions targets.

"We know that there is a wrecking crew in Bali led by the U.S. administration and its minions," said Jennifer Morgan, spokeswoman for environmental groups on Bali. "They are working hard to pull out the bits of text that matter to developing countries on finance and technology."

In the end, however, all parties agree it is vital that the U.S. is on board.

"Everyone wants the United States in so badly that they will be willing to accept some level of ambiguity in the negotiations," said Greenpeace energy expert John Coequyt. "Our worry is that we will end up with a deal that is unacceptable from an environmental perspective."

The Kyoto Protocol requires 37 industrial nations to reduce greenhouse-gas emissions by a relatively modest average 5 percent below 1990 levels by 2012.

Bush has argued that the pact would harm the U.S. economy and cutbacks should have been imposed on poorer but fast-developing nations such as China and India.