GLASGOW—Dozens of countries agreed to stop funding new coal-fired power plants, a deal that brings some previous holdouts like Poland and Vietnam aboard a growing coalition of countries vowing to wean their economies off the fossil fuel.

Separately, a group including the U.S., the U.K. and Canada pledged to end public funding of overseas oil and gas developments. Proponents called the two deals, struck at the COP26 United Nations climate summit, significant moves in building a consensus among governments toward ending new...

GLASGOW—Dozens of countries agreed to stop funding new coal-fired power plants, a deal that brings some previous holdouts like Poland and Vietnam aboard a growing coalition of countries vowing to wean their economies off the fossil fuel.

Separately, a group including the U.S., the U.K. and Canada pledged to end public funding of overseas oil and gas developments. Proponents called the two deals, struck at the COP26 United Nations climate summit, significant moves in building a consensus among governments toward ending new fossil fuel investments. Critics said the limited number of countries signing onto both deals could blunt their effectiveness on a global scale.

Both deals leave plenty of room for alternative funding options for developing countries set on continuing building coal-powered plants and developing oil and gas reserves in their countries. But the deals could add pressure on some of these alternative lenders, making investment harder to come by and potentially more expensive.

The two agreements fit into a pattern of deals signed by subsets of like-minded countries pursuing their own, limited emissions-reducing ambitions at COP26, which they hope can pressure other countries to act more aggressively.

“These announcements are raising the bar for everyone, including India and China,” said Lauri Myllyvirta, lead analyst at think tank Centre for Research on Energy and Clean Air. “It has a knock-on effect,”

The two deals come as a broader U.N.-backed agreement on specific, binding emissions-reductions commitments evades delegates so far. Big polluters like China, India and Russia have pledged emissions cuts, but not to the levels that Western nations, like the U.S., the U.K. and members of the European Union, have insisted are necessary to limit global warming.

Ending coal financing has been a key focus of the U.K. government in its role as host of the climate talks. Signatories to the coal deal have agreed to phase out “unabated” coal power—meaning projects that don’t have technology to capture carbon-dioxide emissions—in major economies that have signed on in the 2030s, and for the rest in the 2040s. The U.K. government estimates the deal could result in the closure of 40 gigawatts of coal power, equivalent to over half the U.K.’s electricity generation capacity.

“Today’s ambitious commitments made by our international partners demonstrate that the end of coal is in sight,” said the U.K.’s Business and Energy Secretary Kwasi Kwarteng.

But Thursday’s deal falls significantly short of a global pledge. Leading coal consumers China, India and the U.S. aren’t part of the 40-member group that signed the pledge. Meanwhile, a separate promise by the U.S. and the U.K. to end public funding of oil and gas investments overseas included about 20 signatories.

In that deal, government-backed banks in the U.S., Canada and the U.K. said that they would stop financing unabated coal, oil and natural-gas projects abroad by the end of next year. Priority will instead be given to clean energy projects, according to a statement issued by 20 countries and institutions. The group said they currently spend about $15 billion annually financing such fossil fuel projects.

The announcements come after the Group of 20 major economies agreed on Sunday to stop public financing of new coal-fired power plants abroad by the end of this year. There was no commitment at the G-20 over oil and natural gas.

The largest funders of fossil fuel development abroad, including South Korea, Japan and China, weren’t part of Thursday’s coal, oil and gas agreement. Europe was split. Portugal and the European Investment Bank, a lending arm of the European Union, signed up. Italy, Germany and the European Bank of Reconstruction and Development, a government-funded development bank, didn’t.

The U.S. is one of the more significant spenders on overseas oil and gas projects, through funding to developing countries via organizations like the Export-Import Bank and the International Development Finance Corp. Last year, for instance, the U.S. Export-Import Bank provided a $75 million credit guarantee facility to Argentina’s state-run oil-and-gas company YPF SA, which included the purchase of equipment from U.S. companies.

Money is a sticking point in climate-change negotiations around the world. As economists warn that limiting global warming to 1.5 degrees Celsius will cost many more trillions than anticipated, WSJ looks at how the funds could be spent, and who would pay. Illustration: Preston Jessee/WSJ The Wall Street Journal Interactive Edition

Write to Sarah McFarlane at sarah.mcfarlane@wsj.com and Sha Hua at sha.hua@wsj.com