No, I never thought about Syrian president Bashar al-Assad's assassination: Donald Trump

US President Donald Trump on Wednesday said he did not discuss assassinating Syrian leader Bashar al-Assad, disputing an account in a forthcoming book by journalist Bob Woodward.

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 Defence 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 is 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."