Prospects for a comprehensive climate treaty appeared to take a small step forward Saturday as diplomats neared agreement on a plan that for the first time commits all countries to addressing the causes of global warming.

Haggling over final details of the plan continued late into Saturday evening, more than 24 hours after the negotiations in Lima, Peru, were scheduled to end. But U.S. and European officials said the talks had already yielded important progress that could help pave the way for a final treaty on cutting greenhouse gases late next year.

"If things continue to progress, it will be a significant advance," said a U.S. official familiar with the negotiations, who spoke on the condition of anonymity because sensitive discussions were still underway.

Negotiators from more than 190 countries have huddled since Dec. 1 to begin deciding the shape of next year's proposed treaty, including how costs and obligations will be divided among poorer and wealthier countries. Despite numerous clashes that came close to derailing the talks, diplomats were nearing approval on a formula that spells out rules governing how countries will seek to curb emissions after 2020, participants in the talks said late Saturday.

In a key advance over previous climate accords, all countries would submit a detailed plan for reducing carbon emissions, with the individual plans becoming the basis for an international treaty to be finalized late next year in Paris. In the past, developing countries, including major emitters such as China and India, were exempted from mandatory cuts in greenhouse-gas pollution.

Environmental groups and some independent observers were disappointed, saying that the requirements were excessively watered down and that most of the difficult decisions were left unresolved. They are to be taken up in the months before negotiations on a final treaty begins next December.

"The current text simply ignores the key points of contention between developed and developing countries, in the name of keeping everyone at the table," said Paul Bledsoe, who is a former White House official on climate under President Bill Clinton and who is attending the talks in Lima. "All the toughest issues will still have to be resolved over the next year ahead of any potential Paris agreement."

The Obama administration promised last month to reduce U.S. emissions by 2025 to a level 26 percent to 28 percent below where they were in 2005.

The talks went into overtime Saturday as delegations clashed over demands by developing countries for compensation from industrialized countries for damage from climate change as well as demands for more financial assistance to pay for a transition to climate-friendly energy sources.

The slow progress prompted Secretary of State John Kerry to fly to Lima on Thursday to urge negotiators along.

"If we continue down the same path we are on today, the world as we know it will profoundly change, and it will change dramatically for the worse," Kerry told a gathering of diplomats at the United Nations-sponsored talks.

Pope Francis also weighed in, warning diplomats in a statement that "the time to find global solutions is running out."

"We can find solutions only if we act together and agree," the pontiff said in a message sent to environment minister Manuel Pulgar Vidal, the Peruvian official chairing the talks.