President Donald Trump is expected to pull the United States from a landmark global climate agreement, a White House official said Wednesday, though there could be "caveats in the language" announcing a withdrawal, leaving open the possibility that his decision isn't final.

Exiting the deal would be certain to anger allies that spent years negotiating the accord to reduce carbon emissions.

The official insisted on anonymity in order to discuss the decision before the official announcement.

Trump tweeted on Wednesday morning: "I will be announcing my decision on the Paris Accord over the next few days. MAKE AMERICA GREAT AGAIN!"

Nearly 200 nations, including the United States under President Barack Obama's administration, agreed in 2015 to voluntarily reduce their greenhouse gas emissions in an effort to combat climate change. Withdrawing would leave the United States aligned only with Russia among the world's industrialized economies in rejecting action to combat climate change.