Britain said Wednesday it would join the United States in a charge to curb financial aid for building coal-fired power plants abroad.

The announcement was made at UN climate talks in Warsaw where the fossil fuel -- the biggest single contributor to global warming -- has been at the centre of a storm.

"The UK will join the United States in agreeing to end support for public financing of new coal-fired power plants overseas, except in rare circumstances," Ed Davey, Britain's energy secretary, told journalists in Warsaw.

"The two governments are going to work together to secure the support of other countries, and there are other countries who are already up to this... and the multilateral development banks to adopt similar policies."

Last month, the United States said it would end most financing of coal projects overseas to help brake climate-altering greenhouse gas emissions.

The decision put into action one of the pledges President Barack Obama made in announcing a new climate initiative in June.

UN chief Ban Ki-moon on Wednesday urged "much bolder" spending on measures to stave off climate change, which he called the "greatest single threat to peace, prosperity and sustainable development."

"The rapid development of low-carbon infrastructure needs large injections of public capital," he said.

The International Energy Agency (IEA) says coal accounted for 44 percent of carbon dioxide (CO2) emissions in 2011, the largest share, and remains the leading source of electricity and heat generation.

Poland, the world's ninth-biggest producer of the commodity in 2012 according to the IEA, raised the ire of many this week with its "endorsement" of a global coal summit held in the same city hosting the annual round of UN climate negotiations.

The climate talks seek to pave the road to a new, global climate pact by 2015 on limiting climate change through emissions curbs.

UN climate chief Christiana Figueres addressed the coal summit on Monday, urging the industry to make dramatic changes to reduce its emissions.

Having powered the economic growth of the West ever since the Industrial Revolution, the biggest rise today is in developing countries with plentiful, cheap reserves.

United States climate envoy Todd Stern "commended" Davey's announcement, but green groups urged stronger action.

"The UK government should also act to stop UK private finance supporting coal -- regulating the finance sector is our only hope of keeping the coal in the ground," the World Development Movement's Hannah Griffiths said in a statement.

"Until we can cure the private finance sector of its coal addiction, coal will carry on cooking the planet thanks to UK money."

The World Resources Institute (WRI) observer group says nearly 1,200 new coal-fired power plants have already been scheduled for development worldwide -- more than three-quarters of them in India and China.