The US President has insisted Mr Comey, who he fired earlier this week, assured him at a dinner in January that he was not personally under investigation for collusion with Russia before the election.
Intelligence sources have questioned whether any senior investigator would make such a guarantee about an active investigation that the bureau calls “highly significant”.
But Mr Trump tweeted: “James Comey better hope that there are no “tapes” of our conversations before he starts leaking to the press!”
It is not clear if Mr Trump is suggesting his conversations in the White House are being recorded either at his instruction or those of the FBI director.
It was recordings of phone calls and conversations at the White House during Richard Nixon’s presidency that played a part in forcing his resignation over the Watergate scandal. Mr Nixon had asked for the recording system to be installed.
James Comey better hope that there are no “tapes” of our conversations before he starts leaking to the press!
— Donald J. Trump (@realDonaldTrump) May 12, 2017
Mr Trump also defended his media team over criticism at their handling of this week’s event – and threatened to abandon the policy of holding daily press briefings.
He tweeted: “As a very active President with lots of things happening, it is not possible for my surrogates to stand at podium with perfect accuracy.
“Maybe the best thing to do would be to cancel all future “press briefings” and hand out written responses for the sake of accuracy???”
The White House – and even vice-president Mike Pence – had insisted Mr Comey was fired on the recommendation of assistant attorney general Rod Rosenstein because of a loss of trust earlier this week.
But in an interview with NBC News, the President confirmed he was going to dismiss the director irrespective of Mr Rosenstein’s memo, accusing Mr Comey of being a “showboat” and a “grandstander”.
Mr Trump also admitted the “Russia thing” was on his mind in making his decision, calling the allegations of collusion between his campaign and Russia was a “made up story”.
The FBI has confirmed an investigation is continuing and a number of congressional committees are also looking into the Russian connection.
At a hearing on Capitol Hill on Thursday, the acting FBI director Andrew McCabe contradicted White House claims that Mr Comey had lost the support of rank-and-file staff. He also dismissed their claims the investigation was a small matter.
He said there had been no attempt to impede the investigation and that he believed it would be unaffected by Mr Comey’s departure.
In a report on that dinner in January, the New York Times claimed Mr Trump had asked Mr Comey for his “loyalty” but that the director would only offer his “honesty”.
The dinner took place just after the White House had been warned by the then attorney general that Mr Trump’s national security advisor Michael Flynn had been “compromised” and was vulnerable to blackmail over ties to Russia.
At a hearing last week, Mr Comey denied under oath ever leaking information to the media.