US President Donald Trump punched back Friday against James Comey, accusing the ousted FBI director of lying about their private conversations -- and saying he is "100 percent" willing to testify under oath.

Comey delivered scathing testimony a day earlier in a highly anticipated Senate hearing, saying Trump sought to derail a probe into onetime national security advisor Michael Flynn -- at best, a political miscalculation, and at worst a criminal obstruction of justice.

Trump was addressing reporters at the White House for the first time since Comey's explosive appearance, in which he branded the president a liar and said he believed he was fired over his handling of the FBI probe into Russian election meddling.

"Yesterday showed no collusion, no obstruction," Trump said in reference to the twin controversies dogging his administration -- accusations his aides colluded with the Russian effort to tilt the vote, and that he sought to block the related Flynn probe.

Trump lashed out at Comey, dubbing him a "leaker" for indirectly providing reporters with the contents of his memos summarizing their private conversations in the weeks before he was sacked. A person close to Trump's legal team has said a complaint would be filed with the Justice Department.

"Some of the things that he said just weren't true," added the president, who -- when asked if he would be willing to speak under oath to special prosecutor Robert Mueller about the encounters -- responded: "100 percent."

"I would be glad to tell him exactly what I just told you," Trump said.

The White House has seized on Comey's confirmation that Trump personally was not under investigation over his ties to Russia to declare a victory of sorts.

The Republican president took to twitter earlier in the day, claiming "total and complete vindication."

The Trump administration has also highlighted the fact Comey stopped short of accusing the president of obstructing justice -- a potentially impeachable offense. The former FBI chief has said the decision was now in the hands of special counsel Mueller.

Questioned about Comey's central claim that Trump told him to lay off Flynn, the president responded: "I didn't say that."

"And there would be nothing wrong if I did say it, according to everybody that I read today."

Tapes?

During almost three hours of statements Thursday before the Senate Intelligence Committee, Comey described himself as "stunned" by Trump's "very disturbing" and "very concerning" behavior towards him.

Detailing one-on-one talks with a sitting president -- which under normal circumstances are private -- Comey said he took painstaking notes for fear Trump might "lie" about the unusual encounters.

And Comey admitted that he asked a friend to leak those notes to a reporter, correctly betting that the details would prompt the appointment of a special prosecutor.

Comey said he did so after Trump suggested in a tweet that their conversations may have been recorded.

Trump demurred when asked whether tapes of his talks with Comey actually exist.

"I'll tell you about that maybe in the very near future," he said.

Meanwhile, the leaders of the House Intelligence Committee, which is also probing Russian election meddling, wrote Comey requesting his notes memorializing his conversations with Trump.

They separately wrote the White House counsel Don McGahn asking whether the recordings exist, and if so, that they be produced to the committee by June 23.

'Inappropriate'

Pundits and legal experts were divided about whether Trump's actions rose to the level of obstruction of justice, a potentially impeachable offense.

But while Republicans have generally continued to back the president, some have begun openly questioning and criticizing his actions.

"It was clear that the president asked Mr Comey to do an inappropriate action, and that was to drop the investigation of General Michael Flynn," Senator Susan Collins told CNN.

"It crossed a boundary that the president should not have crossed."

Bob Inglis, a Republican former congressman who voted to impeach Bill Clinton in 1998, suggested Trump might be in particularly hot water.

"Yes, I was on Judiciary Cmte that impeached Clinton/sent him for trial in the Senate for matters less serious than the ones before us now," Inglis tweeted Friday.

In his testimony, Comey recalled that during a private White House dinner on January 27, the president asked him for "loyalty" and to lay off his former top aide Flynn -- who is under investigation over his Russia ties -- imploring Comey to "let this go."

"I didn't say that," Trump insisted Friday, before heading to his New Jersey golf club in Bedminster where he will spend the weekend. "I hardly know the man. I'm not going to say, 'I want you to pledge allegiance.'"

Trump abruptly fired Comey as director of the Federal Bureau of Investigation on May 9, later admitting that the Russia probe was on his mind at the time.

Harvard Law School professor Mark Tushnet said onlookers should keep in mind that Comey knows much more than he can say, calling his testimony a "big deal."

Lawmakers will get another chance to hear from a top administration official, Attorney General Jeff Sessions, when he testifies Tuesday before the Senate Appropriations Committee.