US President Donald Trump is "wide open" on whether to continue US support for the Paris climate accord, Defence Secretary James Mattis said.

The comments from Mattis, in an interview aired today, come after Trump tweeted yesterday that he would take a decision "next week" on whether to stick to or renege on the climate agreement.

Trump has told several people that he plans to leave the agreement, according to a new report.

Axios reports that Trump has told multiple people, including EPA Administrator Scott Pruitt, that he wants to remove the US from the agreement.

Trump came under intense pressure during meetings with world leaders in Brussels and Italy on the issue.

"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 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 of that accord," Mattis said.

At a meeting of the Group of Seven in Sicily this week, German Chancellor Angela Merkel indicated that Trump's G7 peers lobbied him hard on the issue of climate change.

"We have put forward a lot of arguments" in favour of the Paris deal, she said.

Most reports out of this week's G7 summit saw Trump at odds with the leaders of Britain, Canada, France, Germany, Italy and Japan.

The group managed to agree on language setting goals for trade, but Trump was the lone holdout when it came to agreeing on policies to combat climate change.

Axios: Trump Tells Confidants U.S. is Pulling Out of Paris Climate Change Agreement https://t.co/41vrLTkINr

— Carol Duffie (@songbirdcd) May 28, 2017

Scientists explain apocalyptic effect of Trump pulling out of the Paris climate change agreement https://t.co/7opo7NhjjD

— Independent US (@IndyUSA) May 28, 2017