US President Donald Trump is poised to pull the country out of the Paris climate accord, US media report, quoting senior officials.
The 2015 accord united most of the world in a single agreement to mitigate climate change for the first time.
It was signed by 195 countries out of 197 in a UN group on climate change, with Syria and Nicaragua abstaining.
A source briefed on the decision told Reuters Mr Trump planned to make good on his campaign vow to withdraw the US from the pact.
White House officials cautioned that details were still being hammered out and that, although close, the decision on withdrawing from the 195-nation accord - agreed to in Paris in 2015 - was not finalised.
Mr Trump, In a tweet on Wednesday, said only he would announce his decision within the "next few days".
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
Under the accord, countries agreed to keep global temperatures "well below" the level of 2°C above pre-industrial times and "endeavour to limit" them even more, to 1.5°C.
To date, 147 out of the 197 countries have ratified the accord, including the US, where the accord entered into force last November.
Mr Trump has 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".
His supporters argue the accord restricts America's ability to do what it wants with its energy resources - an important sector of the economy.
However, under the accord, countries set emission limits themselves - not an outside panel.
If Mr Trump does decide to pull out of the accord, it is not clear how he will do it. The agreement stipulates a three-year waiting period before a country can give notice of leaving.
A withdrawal would put the United States in league with Syria and Nicaragua as the world's only non-participants in the Paris agreement.
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.
"The president will make an announcement when he's made a final decision," one senior official told Reuters. Mr Trump has changed his mind on large decisions before, even after previously signaling a move in the opposite direction.
- BBC / Reuters