WASHINGTON — Federal prosecutors suggested on Tuesday that they might ask a federal judge to sentence the former national security adviser Michael T. Flynn to prison as doubts have emerged about whether he honored the cooperation deal he made in his criminal case.

The move was the latest turn in the case of Mr. Flynn, who pleaded guilty in 2017 to lying to F.B.I. agents in the Russia investigation and agreed to cooperate with prosecutors to help make the case that he deserved a light sentence.

[Update: Attorney General William Barr installs an outside prosecutor to review the case against Michael Flynn.]

But in recent months, Mr. Flynn has taken a more aggressive posture. He has hired new lawyers, who accused the government on Tuesday of hiding exculpatory evidence, as they have in court papers.