President Donald Trump is poised to make good on his electoral campaign promise to withdraw the United States from a global pact to fight climate change, a source briefed on the decision says.

White House officials said that details were still being hammered out and that, although close, the decision on withdrawing from the 195-nation accord – brokered in Paris in 2015 – was not finalised.

Mr Trump, who has previously called global warming a hoax, tweeted: “I will be announcing my decision on the Paris Accord over the next few days.”

The source, speaking on condition of anonymity, told Reuters the President was working out the terms of the withdrawal with US Environmental Protection Agency Administrator Scott Pruitt, an oil industry ally and climate change doubter.

I will be announcing my decision on the Paris Accord over the next few days. MAKE AMERICA GREAT AGAIN!

— Donald J. Trump (@realDonaldTrump) May 31, 2017

To date, 147 of the 195 countries have ratified the accord, including the US, where it entered into force last November.

Under the pact, virtually every nation voluntarily committed to combat climate change with steps aimed at curbing global emissions of greenhouse gases such as carbon dioxide generated from burning of fossil fuels that scientists blame for a warming planet, sea level rise, droughts and more frequent violent storms.

It was the first legally-binding global climate deal.

A withdrawal would put the United States in the company of Syria and Nicaragua as the world’s only non-participants in the Paris agreement.

Mr Trump previously called climate change “a hoax” devised by the Chinese government.

He promised to “cancel” the Paris deal during his election campaign last year, saying it was “bad for US business” because it allowed “foreign bureaucrats control over how much energy we use”.

Mr Trump has also said the accord would cost the US economy trillions of dollars without tangible benefit.

The US President refused to endorse the landmark climate change accord at a summit of the G7 group of wealthy nations in Brussels on Saturday, saying he needed more time to decide.

The United States is the world’s second-biggest carbon dioxide emitter behind China.

A shift away from coal to cleaner-burning and cheaper natural gas in recent years has cut US carbon emissions to near 30-year lows, according to the US Energy Information Administration.

A US pullout would be disappointing but the European Union stands ready to take global leadership on the issue, European Commission Vice President Maros Sefcovic said in Brussels.

The European Union and China are working on a joint declaration reaffirming their commitment to climate and energy policy and the implementation of the Paris agreement, according to an EU official with knowledge of the plans.

Supporters of the climate pact are concerned that a US exit could lead other nations to weaken their commitments or also withdraw, softening an accord that scientists have said is critical to avoiding the worst impacts of climate change.

A March Reuters/Ipsos opinion poll found that 50 per cent of Republicans agreed that the US should lead the global fight against climate change, while 37 per cent disagreed and 13 per cent were unsure.

Oil majors Shell and Exxon Mobil have also supported the pact along with a number of Republican lawmakers.

– with AAP