But the sharpest divides remained over who should be required to take on commitments to reduce emissions blamed for global warming.

The world’s environment ministers were working through the night Thursday at the U.N. climate change summit in Mexico as they raced to overcome deep differences by the end of Friday over how to tackle the growing threat of global warming.

In a stock-taking session late Thursday, government ministers reported progress on many new support mechanisms to help poor countries deal with global warming but less success on how to cooperate on cutting global greenhouse-gas emissions.

“Time is running out, and we still have much work ahead of us,” said Mexican Foreign Minister Patricia Espinosa, who is chairing the Cancun summit. But she added, “A broad and balanced package of decisions is indeed within our grasp.” Chairs of various working groups reported a “consensus” on initiatives that would help poor countries adapt to climate change, and “convergence” on the creation of a global climate fund to channel money from wealthy to poor countries. Deals were less certain on protecting forests and improving technology cooperation.

But the sharpest divides remained over who should be required to take on commitments to reduce emissions blamed for global warming.

The row threatened to derail the U.N. summit, and ministers hoped to salvage a deal by late Friday or early Saturday if more negotiations are needed.

“The situation is still in flux,” Jonathan Pershing, the U.S. deputy climate envoy, said late Thursday.

Japan blocked the renewal of the Kyoto Protocol past its expiration in 2012, demanding a treaty that included the United States and China, while Bolivian President Evo Morales led calls for the rich world to keep alive the lone treaty that limits wealthy countries’ emissions of greenhouse gases.

The U.N. gathering of more than 190 ministers and about 20 world leaders was whittled down to a core group of about 50 ministers who met through most of Thursday afternoon and evening, getting down to the tough business of working out an agreement.

“We’re at the phase now of horse trading,” said Elliot Diringer, head of international strategies at the U.S.-based Pew Center on Global Climate Change. “You always have to bring it into a smaller group to finally cut the deals.” Although a new global climate treaty was never in the cards in Cancun, the row over emissions has stalled progress on other key initiatives that were closer to agreement, like incentives for countries to reduce deforestation and more technology cooperation.

“We dare not lose this opportunity in Cancun,” said South African President Jacob Zuma, who would be left to pick up whatever pieces remain of the climate process when he hosts the next climate summit in Durban in December 2011.

The leaders of environmental groups singled out Japan and the U.S. for obstructing progress as activists pleaded with ministers to use the final hours in Cancun to rebuild some trust in the international process after the widely viewed failure of the Copenhagen summit a year ago.

The U.S. was “holding hostage” decisions on climate aid by insisting on greater transparency from developing countries, said Jeremy Hobbs, head of Oxfam International.

The U.S. has argued that increased scrutiny of the climate actions of emerging economies was essential as the wealthy world increases aid for developing countries. New Zealand envoy Tim Groser said countries were working through new proposals on transparency that could “finally prove helpful” in reaching a compromise.

Japan, meanwhile, was sticking to its guns in opposing an extension of the Kyoto Protocol. But Foreign Ministry envoy Akira Yamada said the row shouldn’t block a “concrete outcome” from being reached at the climate summit.

“The Kyoto Protocol issue is not the issue,” Mr. Yamada told reporters in an update on the ongoing talks. “I don’t think this is the main obstacle to these outcomes.” Mr. Yamada noted that Kyoto only covers about one-third of global emissions. Japan was instead pushing for a “single, legally binding agreement” that would include emissions cuts for the U.S. and China, the world’s two biggest emitters.

Mr. Morales, in a 20-minute speech before the conference, urged wealthy governments to rescue the Kyoto Protocol or be responsible for “genocide” by failing to respond to climate change. He warned of the summit becoming “Cancunhagen.” A draft text discussed Thursday, circulated by small island states and supported by the European Union, would see the U.S. and emerging powers commit to working toward their own legally binding treaty, possibly by the South Africa summit.

But a legally binding treaty has been opposed by China while the U.S. has insisted it would only sign up to a treaty that also binds emerging powers. Yamada said there was still “no consensus” on what legal form any future climate treaty should take.