FBI Director James Comey wrote in a memo that U.S. President Donald Trump had asked him to shut down an FBI investigation into ousted national security adviser Michael Flynn, a person familiar with the situation told The Associated Press on Tuesday.

The person had seen the memo but was not authorized to discuss it by name and spoke on condition of anonymity. The existence of the memo was first reported Tuesday by the New York Times.

The White House denied the report.

"While the president has repeatedly expressed his view that General Flynn is a decent man who served and protected our country, the president has never asked Mr. Comey or anyone else to end any investigation, including any investigation involving General Flynn," a White House statement said.

Trump abruptly fired Comey last week, saying he did so based on his very public handling of the Hillary Clinton email probe.

Trump said he fired Comey last week based on his handling of the Hillary Clinton email probe. (Susan Walsh/Associated Press)

But the White House has provided differing accounts of the firing. And lawmakers have alleged that the sudden ouster was an attempt to stifle the bureau's investigation into Trump associates' ties to Russia's alleged meddling in the 2016 presidential election.

Comey's memo detailing his conversation with Trump would be the clearest proof to date that the president has tried to influence that investigation. The Times said it was part of a paper trail Comey created documenting what he saw as Trump's efforts to improperly interfere in the probe.

The U.S. Justice Department declined to comment.

According to the New York Times, Comey wrote in the February memo that Trump told him Flynn had done nothing wrong. (Evan Vucci/Associated Press)

According to the Times, Comey wrote in the February memo that Trump told him Flynn had done nothing wrong.

"I hope you can see your way clear to letting this go, to letting Flynn go," the president said, according to a memo cited in the report. "He is a good guy. I hope you can let this go."

But Comey did not say anything to Trump about limiting the investigation, replying, "I agree he is a good guy."

The newspaper said Comey was in the Oval Office that day with other national security officials for a terrorism threat briefing. When that ended, Trump asked everyone to leave except Comey, and he eventually turned the conversation to Flynn.

Senate renews call for Comey to testify

On Tuesday, for the second night in a row, Senate Republicans and Democrats were caught off-guard as they entered the chamber for a scheduled vote.

"I don't know the facts, so I really want to wait until I find out what the facts are before commenting," Republican Texas Senator John Cornyn told reporters.

Asked if it would be obstructing justice for Trump to have asked Comey to drop the Flynn investigation, Cornyn said: "You know, that's a very serious charge. I wouldn't want to answer a hypothetical question."

Lindsey Graham, chair of the Senate judiciary subcommittee on crime and terrorism, responded to the reports by saying Comey 'should come in and tell us about it.' (Carolyn Kaster/Associated Press)

Senator Lindsey Graham, Republican from South Carolina, emphatically said he's not commenting on news stories anymore.

"Let's get to the bottom of what happened with the director. And the best way to get to the bottom of it, is for him to testify.… I'm not going to take a memo, I want the guy to come in," Graham told reporters, adding, "If he felt confident enough to write it down, he should come in and tell us about it."

Senator Dianne Feinstein, Democrat from California, said Comey needs to come to Capitol Hill and testify.

Just leaving Senate floor. Lots of chatter from Ds and Rs about the exact definition of "obstruction of justice". <a href="https://t.co/zXj32i2x8b">https://t.co/zXj32i2x8b</a> —@ChrisMurphyCT

Senator Mark Warner of Virginia, the top Democrat on the Senate intelligence committee, said he will ask Comey for additional material as part of the panel's investigation. "Memos, transcripts, tapes — the list keeps getting longer," he said.

Democratic Senator Chris Murphy of Connecticut tweeted: "Just leaving Senate floor. Lots of chatter from Ds and Rs about the exact definition of 'obstruction of justice."'

'I have my subpoena pen ready'

The Republican chair of the House oversight committee is requesting that the FBI turn over all documents and recordings that detail communications between Comey and Trump.

Jason Chaffetz of Utah said in a letter to the FBI that he's making the request to determine whether the president attempted to influence or impede the bureau's investigation into Flynn.

.<a href="https://twitter.com/GOPoversight">@GOPoversight</a> is going to get the Comey memo, if it exists. I need to see it sooner rather than later. I have my subpoena pen ready. —@jasoninthehouse

Chaffetz had earlier told the AP the memo raises concerns "about improper interference placed on an active investigation."

Chaffetz said he will use the authority of a congressional subpoena if necessary, and on Twitter wrote, "I have my subpoena pen ready."

There is no sign the FBI's Russia investigation is closing. Acting FBI director Andrew McCabe told Congress last week the investigation is "highly significant" and said Comey's dismissal would do nothing to impede the probe.