US secretary of state Rex Tillerson has defended Donald Trump's fitness for office after the author of a bombshell new book cast doubt of the president's mental health.
Fire and Fury author Michael Wolff yesterday told NBC's Today show that "100%" of the people around Mr Trump questioned the president's intelligence and "fitness for office".
Responding to claims the president has a short attention span, regularly repeats himself and refuses to read briefing notes, Mr Tillerson told CNN that he had "no reason to question his mental fitness."
While defending Mr Trump, Washington's chief diplomat admitted the president has a very different decision making process and Mr Tillerson has spent a lot of time "understanding how to best communicate with him."
"I have to learn how he takes information in, processes it and makes decisions," Mr Tillerson told CNN.
"He is not a typical president of the past, I think that's well recognised - that's also why the American people chose him," he said.
The president has taken to Twitter to vent his wrath at Fire and Fury, which paints an unflattering picture of Mr Trump as an undisciplined man-child who does not understand the weight of the presidency.
In his most recent outburst, Mr Trump called author Mr Wolff a "loser".
He wrote: "Michael Wolff is a total loser who made up stories in order to sell this really boring and untruthful book. He used Sloppy Steve Bannon, who cried when he got fired and begged for his job. Now Sloppy Steve has been dumped like a dog by almost everyone. Too bad!"
White House press secretary, Sarah Sanders dismissed Fire and Fury as "trashy tabloid fiction". On Friday Ms Sanders told Fox and Friends that the author had "repeatedly begged to see the president" but his requests had been refused.
Ms Sanders said Wolff had "made up a lot of stories to try and sell books."
But speaking to Today, Mr Wolff stood by his book and dismissed the White House's claims.
He said: "I absolutely spoke to the president. My window into Donald Trump is pretty significant.
"I work like every journalist works. I have recordings. I have notes. I am certainly and absolutely in every way comfortable with what I have reported."
The row over its publication has helped Fire and Fury become an instant best-seller, with bookshops on both sides of the Atlantic selling out of their copies within minutes.