White House Press Secretary Sarah Huckabee Sanders on Wednesday called former White House strategist Steve Bannon's claim that Donald Trump Jr.'s meeting with Russians in June 2016 was "treasonous" a "ridiculous assertion."

Bannon made the claim in an explosive new book by Michael Wolff, "Fire and Fury: Inside the Trump White House," due out January 9.

"Even if you thought that this [meeting] was not treasonous, or unpatriotic, or bad s---, and I happen to think it's all of that, you should have called the FBI immediately," Bannon told Wolff.

Bannon also said that there was "zero" chance that Donald Trump Jr. did not bring the Russians — whom Trump Jr. initially believed might have damaging information on Democrat Hillary Clinton — up to his father's office to say hello after their meeting on June 9, 2016.

Sanders on Wednesday denied that President Donald Trump knew anything about the meeting at the time it happened. "As the president has stated many times, no, he wasn't part of that [meeting] or aware of it," she said.

The book's revelations have driven a vicious wedge between the president and Bannon, his onetime closest adviser.

"Going after the president's son in an absolutely outrageous and unprecedented way is probably not the best way to curry favor with anybody," Sanders said of Bannon's comments about Donald Trump Jr.

Earlier in the day, the president issued a statement saying that when Bannon was fired from the White House last summer, "he not only lost his job, he lost his mind."

Speaking to reporters, Sanders said the president was both "furious" and "disgusted" by the outrageous claims Wolff reported in the book, copies of which were acquired by news organizations on Wednesday.

Yet Sanders also acknowledged that Trump has kept in touch with Bannon by phone since the former chief strategist left the White House in the summer of 2017. Their most recent conversation, Sanders said, was in early December.