President Trump called Bob Woodward's new tell-all book a "work of fiction" and said he did not discuss the assassination of the Syrian leader Bashar al-Assad.

According to excerpts from the book, "Fear: Trump in the White House," Trump told Mattis that he wanted to have Assad assassinated after the Syrian president launched a chemical attack on civilians in April 2017.

Mattis told Trump he would "get right on it," but instead developed a plan for a limited air strike that did not threaten Assad personally.

Trump, speaking to reporters during a visit with Kuwaiti ruler Sheikh Sabah al-Ahmad al-Jaber al-Sabah, said a possible assassination was "never even discussed."

"That was never even contemplated, nor would it be contemplated," Trump said, calling Woodward's book "fiction."

Trump wanted to have Assad assassinated last year but Defense Secretary James Mattis ignored the request, according to the book "Fear: Trump in the White House." Excerpts were published by the Washington Post on Tuesday.

Trump also said that if there were a slaughter in the Idlib province of Syria, the United States will be very angry. The Syrian military shelled Idlib, the last stronghold of active rebellion against al-Assad, on Wednesday as a war monitor said insurgents blew up a bridge in anticipation of a government offensive.

"That cannot be a slaughter," Trump said about Idlib. "If it is a slaughter the world is going to get very, very angry and the United States is going to get very angry too.”