Donald Trump's former chief strategist Steve Bannon has slammed the US president's son for holding a meeting with Russian officials during the 2016 election campaign in an explosive new book.

Bannon has described the meeting between Donald Trump Jr. and a group of Russians, including Kremlin lawyer Natalia Veselnitskaya, as "treasonous" and "unpatriotic" in a new book seen by The Guardian.

Michael Wolff's book Fire and Fury: Inside the Trump White House features an interview with the Breitbart boss in which he predicts that the ongoing investigation into the Trump campaign's alleged collusion with the Kremlin will focus on money laundering.

Bannon, who was chief executive of the Trump campaign in its final three months, told Wolff that Trump Jr. will "crack like an egg" under the pressure of the investigation.

He was particularly scathing about the meeting Trump Jr. held with Veselnitskaya, his brother-in-law Jared Kushner and then campaign chairman Paul Manafort at Trump Tower 2016.

In a series of emails sent before the meeting, British publicist Rob Goldstone told Trump Jr. that Veselnitskaya had agreed "to provide the Trump campaign with some official documents and information that would incriminate Hillary and her dealings with Russia."

Wolff writes that Bannon mocked Trump Jr.'s decision to take part in the meeting.

"The three senior guys in the campaign thought it was a good idea to meet with a foreign government inside Trump Tower in the conference room on the 25th floor – with no lawyers. They didn't have any lawyers," Bannon told Wolff.

"Even if you thought that this was not treasonous, or unpatriotic, or bad shit, and I happen to think it's all of that, you should have called the FBI immediately."

Bannon said that such a meeting should have taken place at a Holiday Inn in Manchester, New Hampshire, with your lawyers who meet with these people," Wolff writes.

After President Trump dismissed James Comey as FBI director, special counsel Robert Mueller was appointed to lead the Russia investigation. Four members of Trump's inner circle, including Manafort and his former national security adviser Michael Flynn, have been indicted.

In an interview with The New York Times last week, Trump said that he believes Mueller will treat him fairly.

"It makes the country look very bad, and it puts the country in a very bad position. So the sooner it's worked out, the better it is for the country," Trump said of the investigation.

Steve Bannon speaks at CPAC
Donald Trump's former chief strategist Steve Bannon has described the meeting between the president's son and Russian officials in June 2016 as "treasonous" and "unpatriotic."