Donald Trump has hit back at a sharply critical book by James Comey, calling the former FBI director an "untruthful slime ball".
The president reacted on Twitter the day after details emerged from Mr Comey's memoir, and said it was "an honour" to fire him from his post at the FBI.
The book says Mr Trump is "untethered to truth", and describes him as fixated in the early days of his presidency on having the FBI debunk salacious rumours he said were untrue but that could distress his wife.
The book, A Higher Loyalty, is to be released next week.
In the book, Mr Comey compares Mr Trump to a mafia don and calls his leadership of the country "ego driven and about personal loyalty".
He also reveals new details about his interactions with Mr Trump and his own decision-making in handling the Hillary Clinton email investigation before the 2016 election.
He casts Mr Trump as a mobster-like figure who sought to blur the line between law enforcement and politics and tried to pressure him personally regarding his investigation into Russian election interference.
The book adheres closely to Mr Comey's public testimony and written statements about his contacts with Mr Trump and his growing concern about his integrity.
It also includes strikingly personal jabs that appear sure to irritate the president.
The 6ft 8in Mr Comey describes Mr Trump as shorter than he expected with a "too long" tie and "bright white half-moons" under his eyes that he suggests came from tanning goggles.
He also says he made a conscious effort to check the president's hand size, saying it was "smaller than mine but did not seem unusually so".
"Donald Trump's presidency threatens much of what is good in this nation," Mr Comey writes, calling the administration a "forest fire" that cannot be contained by ethical leaders in the government.
On a more personal level, Mr Comey describes the president repeatedly asking him to consider investigating an allegation involving Mr Trump and Russian prostitutes in a Moscow hotel, to prove it was a lie.
Mr Trump has strongly denied the allegation, and Mr Comey says it appeared the president wanted it investigated to reassure his wife Melania.
The president fired Mr Comey in May 2017, setting off a scramble at the Justice Department that led to the appointment of Robert Mueller as special counsel overseeing the Russia investigation.
Mr Mueller's probe has expanded to include whether Mr Trump obstructed justice by firing Mr Comey, which the president denies.
The president has assailed Mr Comey as a "showboat" and a "liar".
Senior White House aides also criticised the fired FBI director on Friday.
White House spokeswoman Sarah Huckabee Sanders questioned his credibility in a tweet and White House counsellor Kellyanne Conway said he took "unnecessary, immature pot shots".
