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.
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.
Once over dinner and twice over the phone, Mr Comey had told him he was not a target of the inquiry, the US president said.
His comments raised accusations among opponents that he 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 did it take so long?
Donald Trump was reportedly unhappy with how his press team handled fallout from Tuesday's decision to fire Mr Comey, so he's taken things into his own hands. Boy, has he.
First he gave an interview that essentially undercut all the arguments White House officials, from Vice-President Mike Pence on down, had made to paint the Comey sacking as an operation conducted through normal channels. Now he has taken to Twitter in earnest, spraying a barrage of allegations, accusations and aggressions against Democrats, the media and Mr Comey himself.
In sports terms, the strategy could be described as "flooding the zone" - launching a ferocious, full-out assault to overwhelm an opponent's defences. In this case, Mr Trump has the media scrambling to decide which story merits the most coverage.
Is it the details of the Comey-Trump dinner and the president's hints of secret "tapes"? His threat to cancel press briefings? The Oval Office visit by a Russian entourage? Perhaps, as Mr Trump suggests, the "real news" is the tentative trade agreement between the US and China on beef and poultry products?
When everything is a big story, nothing is. At least, that's what Mr Trump may hope.
There is also a suggestion Mr Comey had asked for more resources for the FBI inquiry.
Then there is a New York Times report this week which 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.
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???"
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.
But the reference has done nothing to silence the echoes of the Watergate affairthat 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.
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.
In another tweet on Friday, Mr Trump said: "When [former Director of National Intelligence] James Clapper himself, and virtually everyone else with knowledge of the witch hunt, says there is no collusion, when does it end?"
However, 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.
Separately on Friday, Mr Trump's lawyers said a review of the past 10 years of his tax returns showed "no income of any type from Russian sources". Although there was income from a beauty pageant and the sale of a property, there was "no equity investment by Russians" and no money owed by Russians to Mr Trump, a letter said.