WASHINGTON -- President Trump said in a tweet early Sunday that he never asked former FBI Director James Comey to stop investigating his ex-national security adviser, Michael Flynn, issuing a fresh denial amid a shifting timeline on when he may have known that Flynn had lied to the FBI.

"I never asked Comey to stop investigating Flynn," Mr. Trump said on Twitter before dawn. "Just more Fake News covering another Comey lie!"

The president reiterated his version of events after Comey testified before Congress in June that Mr. Trump had asked him in a one-on-one meeting if he could see to "letting Flynn go."

I never asked Comey to stop investigating Flynn. Just more Fake News covering another Comey lie! — Donald J. Trump (@realDonaldTrump) December 3, 2017

Mr. Trump shifted his story Saturday on why he fired Flynn, lumping in the retired Army lieutenant general's lies to the FBI along with his untruthfulness with Vice President Mike Pence. The president's initial explanation was that Flynn had to go because he hadn't been straight with Pence about contacts with Russian officials.

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Lying to the FBI is a crime, and one that Flynn acknowledged Friday in pleading guilty and agreeing to cooperate with the special counsel's Russia investigation.

Mr. Trump tweeted Saturday: "I had to fire General Flynn because he lied to the Vice President and the FBI. He has pled guilty to those lies. It is a shame because his actions during the transition were lawful. There was nothing to hide!"

I had to fire General Flynn because he lied to the Vice President and the FBI. He has pled guilty to those lies. It is a shame because his actions during the transition were lawful. There was nothing to hide! — Donald J. Trump (@realDonaldTrump) December 2, 2017

Amid questions raised by the tweet, Trump associates tried to put distance Saturday evening between the president himself and the tweet.

Sources with direct knowledge of the situation told CBS News that Mr. Trump's personal attorney composed the tweet that implied Mr. Trump knew Flynn had lied to the FBI when he demanded his resignation in February. John Dowd was the principal wordsmith for the tweet, and it's unclear if Mr. Trump saw the final version, sources said. The president was in between fundraisers in New York when the tweet was sent from an iPhone.

In another email wrinkle in the investigation into Mr. Trump's ties to Russia, The New York Times reported Saturday that emails among top Trump transition officials suggested that Flynn was in close contact with other senior members of the transition team before and after he spoke to Russian Ambassador Sergey Kislyak. A Dec. 29 email from K.T. McFarland, a transition adviser to Trump, suggested that Russian sanctions announced by the Obama administration had been aimed at discrediting Mr. Trump's victory.

She wrote the sanctions could also make it more difficult for Mr. Trump to ease tensions with Russia, "which has just thrown the U.S.A. election to him," she wrote in the emails obtained by the Times. A White House attorney told the newspaper McFarland only meant that Democrats were portraying it that way.

It's unclear why Mr. Trump would cite lying to the FBI as a reason for firing Flynn. Doing so suggests the president knew at the time that Flynn had done something that is against the law, and therefore the investigation could not be as frivolous as he's been portraying. It's also unclear how he would know that, if information about Russian contacts had not reached him, as he has been implying in his own defense.

Sources told CBS News that Dowd meant to convey that Flynn was fired for lying to Pence and other White House officials about his conversations with Kislyak, and "now we know" that he lied to the FBI, according to the sources. But Dowd bungled the tweet and created confusion around Mr. Trump's knowledge of events.

U.S. President Donald Trump speaks to the media before departing the White House on Marine One, on December 2, 2017, in Washington, D.C. Mark Wilson/Getty Images

Flynn left the White House in February, only acknowledging that he had given an incomplete account to Pence of his conversations with Kislyak. After Mr. Trump forced Flynn out, he asked Comey to end the bureau's probe in the matter, according to Comey's account. Comey refused, and Mr. Trump fired him, too.

Then-White House spokesman Sean Spicer said after Flynn's firing that it was the result of a "trust issue" and the White House counsel's office had determined there was not a legal issue.

"Whether or not he actually misled the vice president was the issue, and that was ultimately what led to the president asking for and accepting the resignation of Gen. Flynn," Spicer told reporters on Feb. 14. "That's it, pure and simple. It was a matter of trust."

Mr. Trump has been publicly dismissive of Comey and of special counsel Robert Mueller's continuing investigation, and was often generous in his appraisal of Flynn, except to say his adviser could not stay on the job after misleading his vice president.

At the time, Pence said Mr. Trump was justified in firing Flynn because Flynn had lied to him. Neither Mr. Trump nor Pence indicated concern then that the FBI had not been told the true story.

Pence, who served as head of Mr. Trump's transition, has not publicly commented on Flynn's plea.

Later Saturday night, Mr. Trump railed about why Flynn was prosecuted but his Democratic opponent Hillary Clinton was not for her alleged misdeeds.

He tweeted: "So General Flynn lies to the FBI and his life is destroyed, while Crooked Hillary Clinton, on that now famous FBI holiday 'interrogation' with no swearing in and no recording, lies many times...and nothing happens to her? Rigged system, or just a double standard?"

He then added: "Many people in our Country are asking what the 'Justice' Department is going to do about the fact that totally Crooked Hillary, AFTER receiving a subpoena from the United States Congress, deleted and 'acid washed' 33,000 Emails? No justice!"

Clinton was voluntarily interviewed for more than three hours at FBI headquarters in July 2016. She was not in custody during her interview and so, in accordance with standard FBI and Justice Department protocol, her interview would not have been recorded. A Justice Department policy on recorded interrogations applies to individuals who have been arrested and are in custody.

It is nonetheless a crime to lie to the FBI about any material fact in an investigation. Comey has said Clinton did not lie to the FBI during her interview.

Early Sunday, Mr. Trump again appeared critical of the Comey-led FBI in light of the lack of charges against Clinton, saying "After years of Comey, with the phony and dishonest Clinton investigation (and more) running the FBI, its reputation is in tatters -- worst in History!"

He added, "But fear not, we will bring it back to greatness."

After years of Comey, with the phony and dishonest Clinton investigation (and more), running the FBI, its reputation is in Tatters - worst in History! But fear not, we will bring it back to greatness. — Donald J. Trump (@realDonaldTrump) December 3, 2017

Mr. Trump also took a shot at ABC News, after an ABC News reporter who erroneously reported a crucial detail following Flynn's guilty plea was suspended for a month without pay.