U.S. President Donald Trump said on Thursday his former national security adviser, Michael Flynn, was tormented by "dirty cops" as part of the probe into whether Russia helped Trump win the White House in 2016.

The president's comments in the Oval Office, latest in a string of remarks about Flynn, may suggest that the retired general could be in line for a presidential pardon.

Flynn pleaded guilty to making false statements in a charge brought by then-Special Counsel Robert Mueller. He is now insisting he did not lie and wants to back out of the plea.

Internal FBI documents turned over by the Justice Department on Wednesday showed FBI officials debated whether and when to warn Flynn that he could face criminal charges as they prepared for a January 2017 interview with him in the Russia probe.

Trump blamed Flynn's predicament on "dirty cops" and said the documents show Flynn is a victim.

“He’s in the process of being exonerated. If you look at those notes from yesterday, that was total exoneration," Trump said.