President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE on Wednesday denied that he had discussed killing Syrian President Bashar Assad, one day after it was reported in Bob Woodward's forthcoming book that he had pushed for Assad to be assassinated in a conversation with his defense chief.

"Not at all. The book is fiction," Trump told reporters when asked about the claim, saying the assassination of Assad was "never even discussed."

"No, that was never even contemplated, nor would it be contemplated and it should not have been written about in the book," Trump added.

The president lashed out at Woodward's book repeatedly during a meeting with the emir of Kuwait.

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The first excerpts from Woodward's book, "Fear: Trump in the White House," were published on Tuesday, and painted a portrait of a White House rife with infighting and undergoing a "nervous breakdown."

Woodward wrote that in April 2017, following a chemical attack on civilians in Syria, Trump urged Mattis that the U.S. should “f--king kill” Assad.

Mattis reportedly went along with the president’s demands during the phone call, but immediately told aides after hanging up that they would take a “much more measured” approach.

Mattis issued a statement Tuesday night denying he ever said or heard the quotes attributed to him in the book excerpts published Tuesday.

Trump's comments about Assad come as the U.S. continues to monitor heightened tensions in Syria's Idlib province, which is the last major rebel stronghold in the country.

The Trump administration on Tuesday warned Assad against using chemical weapons on his citizens, hours after Syria's ally, Russia, struck Idlib.

Russian planes targeted the northwestern province with roughly 30 airstrikes earlier Tuesday. The strikes were accompanied by Assad's artillery, killing at least 17 civilians, including five children, The Wall Street Journal reported.

Trump on Wednesday called it a "very sad situation," and warned those involved in the conflict to be "very, very judicious and careful."

"That cannot be a slaughter," Trump said, warning that if it becomes one, "the United States is going to get very angry."