US President Donald Trump lashed out at a bombshell-filled book that hits the shelves on Friday, dismissing it as "full of lies" after threats of legal action failed to block its release.

Publishers responded to a cease-and-desist letter by moving forward by four days the release of "Fire and Fury: Inside the Trump White House" - an expose by author Michael Wolff that quotes key Trump aides expressing serious doubt about his fitness for office.

"Look at this guy's past and watch what happens to him and Sloppy Steve!" Trump tweeted - a possible reference to Steve Bannon, his former chief strategist, or Steve Rubin, the publisher of Wolff's book.

The book - which paints Trump as mentally unstable and far out of his depth - includes extensive quotes from Bannon, who also received a "cease and desist" order from Trump's attorneys.

"Your publication of the false/baseless statements about Mr. Trump gives rise to, among other claims, defamation by libel, defamation by libel per se, false light invasion of privacy, tortious interference with contractual relations, and inducement of breach of contract," Trump's lawyers said in the letter to Wolff.