President Donald Trump is reportedly set to pull the United States out of the Paris climate accord, according to several US news reports, dealing a giant setback to efforts aimed at cutting global emissions.

Multiple sources confirmed to news agencies and US broadcasters on Wednesday the decision of the American leader, who later posted on social media that he would make an announcement this week.

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

Trump, who has previously called global warming a hoax, refused to endorse the landmark climate change accord at a summit of the G7 group of wealthy nations on Saturday, saying he needed more time to decide.

Fox News, Axios, the Associated Press and Reuters news agency cited unnamed sources confirming the pullout.

Al Jazeera's James Bays, reporting from Washington, DC, said that no official announcement was expected on Wednesday, adding that "it is worth cautioning" that there are disagreements among his advisers on how to proceed with the deal.

"So until we have the final words of the president, I don't think we should jump the gun. But it is looking like he is going to pull out."

A decision to withdraw from the deal would put the US in league with Syria and Nicaragua as the world's only non-participants in the Paris Climate Agreement.

A US withdrawal would have sweeping implications for the deal, which relies heavily on the commitment of big polluter nations to reduce emissions of gases scientists blame for sea level rise, droughts and more frequent violent storms.

The accord, agreed on by nearly 200 countries in Paris in 2015, aims to limit global warming in part by slashing carbon dioxide and other emissions from the burning of fossil fuels.

Under the pact, former US president Barack Obama committed the US to reducing its emissions by 26 to 28 percent from 2005 levels by 2025.

Meanwhile, European Commission President Jean-Claude Juncker said Europe must make clear to the US that quitting the Paris climate agreement is not a straightforward process, and that fully leaving the deal will take years.

"Europe's duty is to say: it's not like that," Juncker told a student conference on the future of Europe organised by the German employers' association BDA.

READ MORE: UN demands more ambition as US weighs climate pullout

"The Americans can't just leave the climate protection agreement. Trump believes that because he doesn't know the details."

In reality, it would take several years for the U.S. to extricate itself from the obligations that flow from having signed the agreement, the head of the European Union's executive arm added.

The US is the world's second-biggest carbon dioxide emitter behind China.

Reacting to news reports of Trump's decision, Samantha Power, President Obama's ambassador to the United Nations, posted on Twitter: "The end of the American Century."

Nancy Pelosi, opposition leader in the House of Representatives, said the decision would be a "stunning abdication of American leadership" and "a threat to the planet".

During Trump's overseas trip last week, European leaders pressed him to keep the US in the pact.

French President Emmanuel Macron spoke with Trump at length about the issue during a meeting in Brussels, and even at the Vatican, Cardinal Secretary of State Pietro Parolin made his own pro-Paris pitch to Trump and his advisers.

But Trump's chief White House economic adviser, Gary Cohn, told reporters during the trip abroad that Trump's views on climate change were "evolving" following the president's discussions with European leaders.

Word of Trump's decision comes a day after the president met with Scott Pruitt, the administrator of the Environmental Protection Agency. Like his boss, Pruitt has questioned the consensus of climate scientists that the Earth is warming and that man-made climate emissions are to blame.

Once in power, Trump and Pruitt have moved to delay or roll back federal regulations limiting greenhouse gas emissions while pledging to revive the long-struggling US coalmines.

What is not yet clear is whether Trump plans to initiate a formal withdrawal from the Paris accord, which under the terms of the agreement could take three years, or exit the underlying UN climate change treaty on which the accord was based.

Senate Majority Leader Mitch McConnell and 21 other Republicans sent Trump a letter last week urging him to follow through on his campaign pledge to pull out of the climate accord. Most of the senators who signed are from states that depend on the continued burning of coal, oil and gas.

There have been influential voices urging Trump not to ditch the Paris accord. Forty Democratic senators sent Trump a letter urging him to stay in, saying a withdrawal would hurt America's credibility and influence on the world stage.

Hundreds of high-profile businesses have spoken out in favour of the deal, including Apple, Google and Walmart. Even fossil fuel companies such as Exxon Mobil, BP and Shell say the US should abide by the deal.