Donald Trump nearly started a conflict with North Korea in early 2018, when he proposed a tweet that "scared the daylights" out of his defence secretary James Mattis, a new book claims.

“This is all about leader versus leader,” said Mr Trump, according to Fear, an upcoming book by legendary Watergate journalist Bob Woodward seen by the Telegraph. “Man versus man. Me versus Kim.”

Woodward reveals that Mr Trump wanted to send a tweet ordering US military dependents – thousands of family members of 28,500 troops - to leave South Korea.

It sent his national security staff into panic mode. A senior figure in the North Korean politburo had already signalled to them that any evacuation would be interpreted in Pyongyang as a precursor to military attack.

Knowing that, Mr Trump’s tweet would effectively be a declaration war and could have provoked Kim into attacking South Korea. The tweet was never sent.

The book also reveals that Mr Trump decided early in his presidency that the United States would stay in Nato, but told Mr Mattis to become its "rent collector".

Following a crunch meeting at the White House, to decide whether Mr Trump was "in or out" of the alliance, the president was persuaded and told Mr Mattis: "You can have your Nato."