Former FBI Director James Comey was a witness in the Mueller investigation and his meeting records on President Trump were of interest in the probe, the bureau said in a court filing over an FOIA request Monday.

What they're saying: "The FBI and the Special Counsel's office have determined that disclosure of the Comey Memos ... could reasonably be expected to adversely affect the pending Russia investigation. The Comey Memos are his contemporaneous notes about incidents that are of interest in that investigation ..."

Details: USA Today journalist Brad Heath first reported the revelations in the case concerning a Freedom of Information Act request by the news outlet and others for Comey's memos.

Go deeper: Timeline: Every big move in the Mueller investigation