BALI, Indonesia — Nobel laureate Al Gore accused the United States on Thursday of blocking progress at the U.N. climate conference, and European nations threatened to boycott U.S.-led climate talks next month unless Washington compromises on emissions reductions.

The former vice president urged delegates to take urgent action to reduce emissions of greenhouse gases blamed for global warming, and told them that the next U.S. president will likely be more supportive of international caps on polluting gases.

“My own country, the United States, is principally responsible for obstructing progress here in Bali,” said Gore, who flew to Bali from Oslo, Norway, where he received the Nobel Peace Prize for helping alert the world to the danger of climate change.

Asked about Gore’s charge, Kristen Hellmer, a member of the American delegation in Bali, said: “The U.S. is being open and working very constructively with the other countries that are here. We are rolling our sleeves up and really working to come up with a global post-2012 framework.”

Earlier, the United Nations warned that time was running out for an agreement aimed at launching negotiations for a successor to the Kyoto Protocol when it expires in 2012 and the talks in Bali were in danger of “falling to pieces.”

The United States, Japan and several other governments are refusing 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.

European nations said they may boycott a U.S.-led climate meeting next month unless Washington compromises.

“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 President 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.”

The European Union and others say the proposed emissions caps 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.

The U.S. invited 16 other major economies, 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.

Gore urged delegates to reach agreement even without the backing of the United States, saying President Bush’s successor, who will take office in January 2009, would likely be more supportive of binding cuts.

“Over the next two years, the United States is going to be somewhere it is not now,” he said. “I must tell you candidly that I cannot promise that the person who is elected will have the position I expect they will have, but I can tell you I believe it is quite likely.”

Gore, who helped in the final negotiation of the Kyoto pact in 1997, also called for implementing a successor agreement two years early, in 2010. The first implementation period of the Kyoto pact expires at the end of 2012.

“We can’t afford to wait another five years,” he said.

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.”

It also noted that that the conference was the start of negotiations for a new climate pact, not the end.

“We don’t have to resolve all these issues ... here in Bali,” said Undersecretary of State Paula Dobriansky, the head of the U.S. delegation.

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 began Dec. 3.

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.

The talks in Bali are scheduled to wrap up Friday.