US President Donald Trump has denied assertions by prominent journalist Bob Woodward in his new book that he ordered the assassination of Syrian President Bashar al-Assad.
Mr Trump said the idea was "never even discussed" with defence officials.
Defence Secretary James Mattis has also denied words attributed to him in Woodward's book.
The book Fear: Trump in the White House depicts a chaotic administration in a "nervous breakdown of executive power".
Mr Trump has already condemned the new work as a "con on the public".
In the book, senior aides are quoted as saying they hid sensitive documents to prevent Mr Trump signing them and as calling him an "idiot" and a "liar".
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Woodward is a widely respected, veteran journalist who helped expose President Richard Nixon's role in the Watergate scandal in the 1970s.
A day after extracts of the book were published in the Washington Post, another daily the New York Times posted an opinion piece attributed to an unnamed senior White House official saying that the root of the administration's problems was Mr Trump's amorality.
The official said many Trump appointees had vowed to thwart the president's "more misguided impulses".
"It may be cold comfort in this chaotic era, but Americans should know that there are adults in the room," the official adds.
"We fully recognise what is happening. And we are trying to do what's right even when Donald Trump won't."
Later in the day, Mr Trump told a meeting of US sheriffs the "gutless editorial" in the "failing New York Times" was a "disgrace".
His spokeswoman, Sarah Sanders, said in a statement about the unnamed writer: "This coward should do the right thing and resign."
What has been said about Assad?
The book says Mr Trump had ordered the Pentagon to arrange the assassination of the Syrian president after a chemical attack on civilians in April 2017 that was blamed on the Syrian government.
"Let's [expletive] kill him! Let's go in. Let's kill the [expletive] lot of them," Mr Trump is reported to have told Mr Mattis.
The book says Mr Mattis acknowledged Mr Trump's request but then, after the conversation, told an aide he would not do "any of that".
But speaking to journalists on Wednesday, the president said: "That was never contemplated, nor would it be contemplated." He went on to describe the book as "fiction".
What else did the president say?
Mr Trump says quotes attributed to Mr Mattis and Mr Kelly were "made up frauds, a con on the public. Likewise other stories and quotes".
He says the book is "already discredited" with "so many lies and phony sources", rejecting an allegation that he had used the terms "mentally retarded" and "dumb Southerner" to describe Attorney General Jeff Sessions.
The statement from Mr Mattis describes the book as "a product of someone's rich imagination".
The statement from Mr Kelly says: "The idea I ever called the president an idiot is not true... He always knows where I stand and he and I both know this story is total BS..."
What else is in the book?
Woodward says chief economic adviser Gary Cohn and White House staff secretary Rob Porter removed documents from the president's desk to keep Mr Trump from signing them.
The documents would have allowed the president to withdraw from the North American Free Trade Agreement and a trade deal with South Korea.
This amounts to an "administrative coup d'état", Woodward says.