US President Donald Trump has warned fired FBI chief James Comey against leaking material to the media.
He tweeted that Mr Comey had "better hope there are no 'tapes' of our conversations", suggesting such tapes, if they existed, might contradict him.
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 Comey, who had been leading an inquiry into possible collusion between Trump election campaign officials and Russia, was fired on Tuesday.
Mr Trump has insisted Mr Comey told him that he was not under investigation.
White House press secretary Sean Spicer later said Mr Trump had nothing more to say on the "tapes" but that the tweet the president had put out was "not a threat" to Mr Comey.
Mr Trump has said that Mr Comey has told him three times that he was not a target of the FBI inquiry, comments that have raised accusations among opponents that the president was interfering in the investigation.
Mr Trump also said this week that he alone was responsible for the decision to sack Mr Comey, calling him a "showboat" and "grandstander".
But this appeared to undermine earlier comments from administration officials that Mr Comey had been fired on the recommendation of Attorney General Jeff Sessions and his deputy Rod Rosenstein.
The first line of Mr Trump's letter sacking Mr Comey refers to a memo written by Mr Rosenstein and says: "I have accepted their recommendation".
But he later told NBC he was "going to fire him regardless of the recommendation".
The White House said Mr Comey was fired over his handling of the Hillary Clinton email affair, but Democrats have asked, if that is the case, why it took so long.
There is also a suggestion Mr Comey had asked for more resources for the FBI inquiry.
A New York Times report this week also said that, during a one-on-one dinner in late January, Mr Trump had asked Mr Comey for a pledge of loyalty but it was not forthcoming.
Former Director of National Intelligence James Clapper told MSNBC on Friday he had spoken to Mr Comey before the dinner, and the FBI head had said he was "uneasy" about it as it might compromise his inquiry.
Mr Spicer later said that the president had not asked for a pledge of loyalty.
Apparently angered by criticism of the different accounts of the sacking, Mr Trump used another of his tweets on Friday to say: "As a very active President with lots of things happening, it is not possible for my surrogates to stand at podium with perfect accuracy!"
He added: "Maybe the best thing to do would be to cancel all future 'press briefings' and hand out written responses for the sake of accuracy???"
Mr Spicer said the president was a "little dismayed" that the attempts of his press team to give out information were being turned into a "game of gotcha" by the media.
It was unclear whether Mr Trump's reference to "tapes" suggested there might be secret recordings of conversations that could be used to challenge any statements by Mr Comey, or whether it was simply a way of warding him off from commenting.
Mr Spicer said he was not aware of any recording of the dinner with Mr Comey.
The reference to tapes has done nothing to silence the echoes of the Watergate affair that have resounded around the Russian interference inquiry.
In 1973, President Richard Nixon sacked Archibald Cox, the Watergate special prosecutor who was seeking access to tapes of presidential conversations that ultimately led to Mr Nixon's resignation.
CNN cited an unnamed source as saying Mr Comey was "not worried about any tapes" Mr Trump may have of their conversations.
Mr Trump has dismissed the FBI investigation as a "charade" and has said Democrats are using "fake news" about collusion with the Russians as an excuse for losing the election.
Mr Comey's successor, acting FBI Director Andrew McCabe, said on Thursday that it remained "a highly significant investigation".
In testimony to the Senate intelligence committee, he also cast doubt on White House claims that Mr Comey had lost the confidence of his staff.
"I can confidently tell you that the vast majority of employees enjoyed a deep and positive connection to Director Comey," Mr McCabe said.