US President Donald Trump has blasted Steve Bannon as having "lost his mind" after a new book quoted his former campaign adviser going after the president's son, Donald Trump Jr.

In Michael Wolff's upcoming Fire and Fury: Inside the Trump White House, Bannon called Trump Jr's infamous meeting with Russian lawyer, Natalia Veselnitskaya,"treasonous" and "unpatriotic".

But a statement released by the White House quoted President Trump as saying that Bannon has "nothing to do" with the presidency.

"When he was fired, he not only lost his job, he lost his mind," Trump said. "Steve was a staffer who worked for me after I had already won the nomination by defeating seventeen candidates, often described as the most talented field ever assembled in the Republican party."

Bannon, who served as Trump's chief strategist for seven months before returning to a position with Breitbart News, is "learning that winning isn't as easy as I make it look," Trump said.

The president added that Bannon had "little to do" with Trump presidential victory and "everything to do" with the Republican party's shocking loss in the Alabama senate race. "Steve doesn't represent my base—he's only in it for himself," the president said.

"Steve pretends to be at war with the media, which he calls the opposition party, yet he spent his time at the White House leaking false information to the media to make himself seem far more important than he was," the statement continues.

"It is the only thing he does well. Steve was rarely in a one-on-one meeting with me and only pretends to have had influence to fool a few people with no access and no clue, whom he helped write phoney books.

"We have many great Republican members of Congress and candidates who are very supportive of the Make America Great Again agenda. Like me, they love the United States of America and are helping to finally take our country back and build it up, rather than simply seeking to burn it all down."

steve bannon
US President Donald Trump with Steve Bannon Mandel Ngan/AFP/Getty Images