Washington (CNN) The White House's chief lawyer told President Donald Trump in January he believed then-national security adviser Michael Flynn had misled the FBI and lied to Vice President Mike Pence and should be fired, a source familiar with the matter said Monday.

The description of the conversation raises new questions about what Trump knew about Flynn's situation when he urged then-FBI Director James Comey to drop the investigation into Flynn and whether anyone in the White House, including the President himself, attempted to obstruct justice. Special counsel Robert Mueller is investigating whether the Trump campaign colluded with Russians, a probe led by Comey until Trump fired him.

White House counsel Donald McGahn told Trump that based on his conversation with then-acting Attorney General Sally Yates, he believed Flynn had not told the truth in his interview with the FBI or to Pence, the source said. McGahn did not tell the President that Flynn had violated the law in his FBI interview or was under criminal investigation, the source said.

The Washington Post first reported that Trump knew Flynn had likely provided inaccurate information to the FBI and Pence.

"I believe the facts exonerate the President and I'm not going to debate these important issues between the White House and the special counsel in the press," White House special counsel Ty Cobb told CNN.

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