(Adds comment by Cummings)
By David Alexander and Susan Heavey
WASHINGTON, May 12 (Reuters) - President Donald Trump warned ousted FBI Director James Comey on Friday against talking to the media, suggesting there might be tapes of conversations between the two men that could contradict his account.
"James Comey better hope that there are no 'tapes' of our conversations before he starts leaking to the press!" Trump said in a string of Twitter posts.
In a report that added to critics' charges that Trump has overstepped the norms of his office, the New York Times reported that the president asked Comey in January to pledge loyalty to him, a request that would undermine the standing of the FBI chief as an independent law enforcer.
On Twitter, Trump appeared to suggest that if Comey gave his version of contacts between them, the administration might produce tapes of conversations, although it was not clear if such tapes exist. The veiled threat added to the storm over Trump's abrupt firing of Comey on Tuesday.
Critics have assailed Trump for dismissing the FBI chief at a time when the agency is investigating alleged Russian meddling in the 2016 U.S. election, and possible collusion between Moscow and the Trump presidential campaign.
The Federal Bureau of Investigation probe and parallel congressional investigations have cast a cloud over Trump's presidency since he took office on Jan. 20, threatening to overwhelm his policy priorities.
Democrats have accused Trump of trying to dent the FBI probe by firing Comey, and have called for a special counsel to investigate the Russia issue.
The New York Times said Comey has told associates he declined to make a pledge of loyalty to Trump when the president requested it as the pair had dinner at the White House just seven days after his inauguration.
Comey instead told the Republican president he could count on his honesty, the Times said.
"It's shocking to the conscience. We've got to address that," said Democratic Representative Elijah Cummings, referring to Trump's behavior with Comey, including the report that the president asked for the FBI director's loyalty.
Trump says Comey had told him three times he was not under investigation in the Russia probe. He said in an interview on Thursday with NBC News that Comey gave him this assurance during a dinner and in two phone conversations.
Comey has not publicly discussed any conversations he has had with Trump. Acting FBI director Andrew McCabe sidestepped a question during a Senate hearing on Thursday on whether he ever heard Comey tell Trump that the president was not the subject of investigation.
The No. 2 Democrat in the Senate, Richard Durbin, slammed the president after Friday's tweets, telling MSNBC that the president is "dangerous because he may be obstructing justice in terms of the investigation ... and secondly his credibility has been destroyed."
Trump also hit back on Friday at media reports questioning the credibility of White House accounts of why Comey was fired, which have changed over the course of the week and threatened an end to regular White House press briefings.
"As a very active President with lots of things happening, it is not possible for my surrogates to stand at podium with perfect accuracy!" Trump said. "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 initially said Trump fired Comey on the recommendation of the two top officials at the Justice Department, Attorney General Jeff Sessions and deputy Attorney General Rod Rosenstein. In the NBC interview on Thursday, Trump said he would have fired Comey regardless of any such recommendations.
The White House has said Comey's firing was unrelated to the Russia probe. On Thursday, Trump told NBC he knew he ran the risk that by firing Comey he would "confuse people" and "lengthen out the investigation" into ties to Russia.
"In fact when I decided to just do it, I said to myself, I said, 'You know, this Russia thing with Trump and Russia is a made-up story, it's an excuse by the Democrats for having lost an election that they should have won," he said.
The president said he never pressured Comey into dropping the FBI probe, and added that there was no "collusion between me and my campaign and the Russians."
U.S. intelligence agencies concluded in January that Russian President Vladimir Putin ordered a campaign of interference in the election aimed at tilting the vote in Trump's favor. Moscow has denied any such meddling.
Writing by Frances Kerry; Editing by Jeffrey Benkoe and Alistair Bell