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”.

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.”