US President Donald Trump has threatened his former chief strategist Steve Bannon with legal action over "defamatory" statements about Mr Trump's son and son-in-law over a meeting with Russians during the 2016 presidential campaign.
Mr Trump cut ties with Mr Bannon on Wednesday, saying his former adviser had "lost his mind" in a blistering statement issued after reports of disparaging comments by Mr Bannon in a forthcoming book, Fire and Fury: Inside the Mr Trump White House by author Michael Wolff.
In the book, Mr Bannon was quoted as describing a June 2016 meeting with a group of Russians at Mr Trump Tower in New York as "treasonous" and "unpatriotic". The meeting, held after the Russians promised damaging information on Democratic presidential candidate Hillary Clinton, was attended by Donald Trump Jr, Mr Trump's son-in-law Jared Kushner and Paul Manafort, who was Mr Trump's campaign manager at the time.
Lawyers for the President sent a cease-and-desist letter to Mr Bannon on Wednesday. They said in the letter that Mr Bannon had breached an agreement by communicating with Mr Wolff about Mr Trump, his family and the campaign and made disparaging remarks about Mr Trump and his family.
"Legal action is imminent," Mr Trump's personal lawyer Charles Harder said in a statement, according to media reports.
The Washington Post reported on Thursday that Harder also sought to block next Tuesday's publication of the book, which offers a lacerating portrait of an accidental presidency and a dysfunctional White House.
A legal notice to Mr Wolff and publisher Henry Holt said Mr Trump's lawyers were pursuing possible charges including libel, the Post reported.
On Thursday, the White House said no personal devices, including mobile phones, would be allowed in the West Wing beginning next week for security purposes. The moves followed the Mr Bannon split but had been considered for some time.
Mr Trump had relied heavily on Mr Bannon, chairman of the right-wing Breitbart News website, for advice in the months leading up to his upset victory in the November 2016 election. He then gave Mr Bannon a strategic role in the White House, where he became a divisive figure before being fired in August. Mr Bannon returned to Breitbart and continued to talk with Mr Trump.
Mr Trump's statement also diminished Mr Bannon's role in the election victory and accused him of leaking to the media.
On Thursday, Mr Bannon told a caller on Breitbart News radio that "nothing will ever come between us and President Mr Trump and his agenda", according to CNN.