Citing three sources with direct knowledge of Trump's plans, the respected news outlet Axios reported on Saturday the American leader has told key advisers he will withdraw the US from the 2015 Paris climate accord.

Axios named the head of the US Environmental Protection Agency Scott Pruitt as one of the "multiple people" informed of Trump's decision.

The news site was formed last year by one of Politico's co-founders and a former chief White House correspondent.

Axios said the decision, if true, would unravel predecessor Barack Obama's climate policies and send a "combative signal" to the rest of the world that global warming isn't one of Trump's priorities.

Read more: Optimism at climate conference, despite US hesitation

The website acknowledged that the billionaire president has changed his mind on several firm campaign promises since taking office in January.

Mattis says president 'curious' to hear arguments

In an interview broadcast on Sunday, Trump's Defense Secretary James Mattis said that Trump has not yet made any decision on the global agreement.

"I was sitting in on some of the discussions in Brussels, by the way, where climate change came up and the president was open, he was curious about why others were in the position they were in, his counterparts in other nations," Mattis told the CBS show "Face the Nation."

"And I'm quite certain the president is wide open on this issue as he takes in the pros and cons," Mattis added.

Trump riles world leaders on climate

Trump told leaders at the G7 group of nations in Italy on Saturday that he would make his decision over whether the US continues to back the climate landmark agreement within the next week. The G7 includes Germany, Britain, Canada, France and Japan.

"I will make my final decision on the Paris Accord next week!" he tweeted from the summit, having previously called global warming "a hoax."

Read more: Investors beg G7 to stick with Paris climate agreement

Trump's lack of commitment to the climate deal, which commits nations to massively reducing carbon emissions to offset the effects of global warming, upset the US's traditional allies including Germany.

German Chancellor Angela Merkel said the G7 talks on climate had been "extremely problematic."

"The entire discussion about climate was very difficult, if not to say very dissatisfying," Merkel told reporters. "There are no indications whether the United States will stay in the Paris Agreement or not."

The landmark climate deal was signed by 195 countries in Paris in December 2016 and came into force 11 months later.

The accord commits nations to keep global temperature rises to below 2 degrees Celsius ((3.6 degrees Fahrenheit) above pre-industrial levels.