In a post to Twitter criticizing a media report late Monday, the president said, "The Amazon Washington Post fabricated the facts on my ending massive, dangerous, and wasteful payments to Syrian rebels fighting Assad."
Trump didn't specify what was wrong with report by the newspaper, which is owned by Amazon founder Jeffrey P. Bezos.
The Washington Post reported last week that Trump decided to end the aid program nearly a month ago after meeting with CIA Director Mike Pompeo and National Security Adviser H.R. McMaster -- before the G20 Summit in Germany.
The Russian government, which backs the Assad regime, has opposed the program started by then-President Barack Obama four years ago.
Officials said the CIA program will likely be phased out "over a period of months." Jordan, which has hosted training sites for the Syrian rebels, is said to support the move.
The White House did not dispute the story last week, and a CIA spokesman declined comment.
On Friday, the leader of U.S. special forces appeared to confirm the end of the program.
"At least from what I know about that program and the decision to end it, absolutely not a sop to the Russians," Army Gen. Raymond Thomas said at a national security forum in Colorado. "It was, I think, based on an assessment of the nature of the program, what we're trying to accomplish, the viability going forward."
He said it was a "tough, tough decision."
After his speech, Thomas told reporters he hadn't confirmed anything and was referring only to "public reporting."