Washington (CNN)Former Trump national security adviser Michael Flynn pleaded guilty Friday to lying to the FBI about conversations with Russia's ambassador and disclosed that he is cooperating with the special counsel's office.

Flynn is the first person inside the Trump administration to be reached by special counsel Robert Mueller's probe, and the developments are a sign that the investigation is intensifying.

In court Friday morning, Flynn's only comments were to answer yes and no to questions from the judge. He told the judge he has not been coerced to plead guilty or been promised a specific sentence.

In a statement, Flynn said he acknowledged that his actions "were wrong, and, through my faith in God, I am working to set things right.

"My guilty plea and agreement to cooperate with the Special Counsel's Office reflect a decision I made in the best interests of my family and of our country. I accept full responsibility for my actions," he said.