Donald Trump's lawyers have tried to stop the publication of a tell-all book about the President who says he no longer talks to his ex-chief strategist Steve Bannon.
A "cease and desist" letter has been sent to author Michael Wolff and his publisher, threatening libel charges over the upcoming book, Fire and Fury: Inside the Trump White House.
In a crackdown on leaks, the Trump administration also announced on Thursday that staff and guests at the White House will not be able to use their personal mobile phones from next week.
Former White House chief strategist Mr Bannon has been under fire after excerpts of Mr Wolff's book were made public on Wednesday.
One of the excerpts included Mr Bannon apparently saying a meeting between Mr Trump's son, Don Jr, and a group of Russians was "unpatriotic" and "treasonous".
In the letter to Mr Wolff, Charles Harder, the famous US defamation and media lawyer, said Mr Bannon's contributions "give rise to numerous legal claims including defamation by libel and slander, and breach of his written confidentiality and non-disparagement agreement with our clients".
He added: "Legal action is imminent."
The letter - which has been published by The Washington Post - demanded the publisher, Henry Holt and Co, "immediately cease and desist from any further publication, release or dissemination of the book" or excerpts and summaries of its contents.
Mr Trump's lawyers have also asked for a full copy of the book as part of their investigation.
The President responded to the accusations on Wednesday by saying his former close confidant had "lost his mind" after losing his White House role last year.
In a statement issued by the White House, rather than his Twitter account, President Trump said: "Steve Bannon has nothing to do with me or my presidency.
"When he was fired, he not only lost his job, he lost his mind."
The President went on to accuse his former ally of "spending his time at the White House leaking false information to the media to make himself seem far more important than he really was".
Despite the vitriol from his former boss, Mr Bannon said he still supports Mr Trump's agenda and called him "a great man".
First Lady Melania Trump's office called the book something which would be found in the "bargain fiction" bin.
The book also claims that Mr Trump never expected to win the 2016 presidential race, but believed his nomination would boost his brand and deliver "untold opportunities".
Mr Bannon, viewed by many as the architect of Mr Trump's campaign, left the White House in August after a string of disagreements with the President and his allies.
The strategist had contradicted Mr Trump's policy on North Korea in a media interview, had taken attention away from the President.
He was viewed by some as a symbol of the far right who could be bad for the former magnate's image.
Fire and Fury: Inside the Trump White House has shot to the top of the Amazon bestseller charts in the US amid the controversy.