WASHINGTON, April 18 (Xinhua) -- Former FBI Director James Comey has said U.S. President Donald Trump's leadership style is "strikingly similar" to that of a mob boss in his new memoir.

Comey appeared Tuesday night on the TV network CBS' "The Late Show" to promote his tell-all memoir "A Higher Loyalty: Truth, Lies and Leadership."

In the book, Comey described people around Trump as having a mob or a "Cosa Nostra" quality.

He told the late-night talk show host Stephen Colbert that "the leadership style is actually strikingly similar."

"I don't mean it in the sense that Donald Trump is out breaking legs or shaking down shop keepers. I mean in the sense that he leads, it's all about the boss," said Comey.

Comey's book hit the shelves on Tuesday. "This president is unethical, and untethered to truth and institutional values," writes Comey. "His leadership is transactional, ego driven, and about personal loyalty."

Last May, Comey was fired by Trump. The firing came as a shock for even many working inside the FBI, and has prompted an uproar of criticism from Democrats.

Comey was appointed as FBI director in 2013, and has been embroiled in controversy during the presidential election in 2016 after announcing an investigation into the emails of Democratic nominee Hillary Clinton days before election day, a move Clinton said was partially the cause of her loss.