Mr Comey revealed the US President asked him “do I look like a guy who needs hookers?” when he confronted him over allegations he was filmed with sex workers in Moscow in 2013.
Speaking to ABC News, he said: “I honestly never thought these words would come out of my mouth, but I don’t know whether the current president of the United States was with prostitutes peeing on each other in Moscow in 2013.”
A dossier compiled by former British intelligence agent Christopher Steele in 2016 claimed the Russian government had secretly filmed Mr Trump with the prostitutes.
Mr Comey revealed the moment he confronted the president about the allegations.
He said: “I started telling him that I had been alerted to information that he had been using a prostitute in Moscow and that the Russians had filmed the episode.
“He started talking about it: “Do I look like a guy who needs hookers?”
Mr Trump brought up the claims with for a second time in January last year, the former director said.
“He said he may want me to investigate it to prove that it didn’t happen and then he said something that distracted me, he said if there’s even a one per cent chance my wife thinks that’s true that’s terrible,” Mr Comey added.
In a series of furious tweets following the interview on Friday Mr Trump branded Mr Comey, who he fired in May last year, “a weak and untruthful slime ball”.
He said: “James Comey is a proven LEAKER & LIAR. Virtually everyone in Washington thought he should be fired for the terrible job he did-until he was, in fact, fired. He leaked CLASSIFIED information, for which he should be prosecuted.
“He lied to Congress under OATH. He is a weak and and untruthful slime ball who was, as time has proven, a terrible Director of the FBI. His handling of the Crooked Hillary Clinton case, and the events surrounding it, will go down as one of the worst “botch jobs” of history. It was my great honor to fire James Comey!”
The interview comes as Mr Comey released explosive tell-all book A Higher Loyalty on the president.