In an interview set “to shock the president”, former FBI director James Comey has reportedly compared Donald Trump to a mob boss.

A clip of the interview, which was released ahead of its full broadcast on Sunday, shows ABC’s George Stephanopoulos ask Mr Comey, “How strange is it for you to sit here and compare the president to a mob boss?”

Mr Comey was fired as head of America’s federal law enforcement agency by Mr Trump last year after he repeatedly refused to promise his loyalty to the billionaire. The White House insists it was triggered by his handling of a 2016 investigation into Hillary Clinton’s private email server.

According to news site Axios, a source present at the filming said the interview was “going to shock the president and his team” and that it would “certainly add more meat to the charges swirling around Trump”.

The source said Mr Comey “told George things that he’s never said before” and that he “answered every question”.

In the clip, Mr Stephanopoulos asks Mr Comey, “Are there things you know, but haven’t said, that could damage Trump?”, “Was President Trump obstructing justice?” and “Should Donald Trump be impeached?”

Mr Comey himself does not speak during the 30 second video.

Last summer, Mr Comey testified the president had asked him to drop an investigation into sacked national security adviser Michael Flynn, and pressured him to declare he was not being investigated as part of Mr Mueller’s probe.

Appearing before the Senate Intelligence Committee, Mr Comey said the president had lied when he claimed to the American public the FBI was in disarray and that agents had lost confidence in him.

“Those were lies, plain and simple,” he said. He said he started taking notes about his meeting with the president as he could not be sure Mr Trump would tell the truth about what was said between them.

Sunday’s ABC interview forms the first part of a high profile press tour for Mr Comey’s book, A Higher Loyalty: Truth, Lies and Leadership, which will be released next week.