US President Donald Trump congratulates Stephen Bannon during the swearing-in of senior staff in the East Room of the White House

An explosive new book claiming to have the inside scoop on President Donald Trump's White House is going on sale early due to "unprecedented demand," the publisher has said.

An attorney for Mr Trump, Charles J Harder had earlier instructed the publisher, Henry Holt, to “immediately cease and desist from any further publication, release or dissemination of the book,” in a letter. Mr Harder said he is pursuing possible libel charges against the book’s author.

Fire and Fury: Inside the Trump White House, a purported tell-all book about Mr Trump’s presidency penned by veteran journalist Michael Wolff, set off a flurry of condemnation from the White House after excerpts were published on Wednesday. Select excerpts claim that Melania Trump was devastated when her husband won the election, and that former presidential adviser Steve Bannon called a 2016 Trump Tower meeting between Donald Trump Jr, the president's son, and a Kremlin-linked lawyer, “treasonous”.

White House Press Secretary Sarah Huckabee Sanders claimed on Thursday the book was ”filled with false and misleading accounts from individuals who have no access or influence with the White House”. On Thursday, she told reporters that the White House had denied more than 30 requests for information from Mr Wolff.

“This book is mistake after mistake after mistake,” she said.

Ms Sanders also responded to a question about suggestions in the book, said to include purported quotes from Mr Bannon, that Mr Trump is mentally unfit to serve as president. She called such suggestions "disgraceful and laughable".

“If we was unfit, he probably wouldn't be sitting there and wouldn't have defeated the most qualified group of candidates the Republican Party has ever seen," Ms Sanders claimed. "This is an incredibly strong and good leader... That's why we've had such a successful 2017," she added.

Mr Trump cut ties with Mr Bannon on Wednesday, saying his former adviser had "lost his mind," in a blistering statement issued after comments attributed to Bannon in the book were made public.

Mr Trump's statement also diminished Mr Bannon's role in the election victory and accused him of leaking to the media. Before joining the campaign, Mr Bannon headed the conservative Breitbart News website and proved to be a divisive figure in the White House. He returned to Breitbart after being fired, although he is reported to have continued to talk with Trump.

Mr Bannon's reaction to the book controversy has been muted. In interviews with Breitbart after the news broke, he called Mr Trump a "great man" and pledged continued support for the president's agenda.