FBI agents searched the home of John Bolton, a former adviser to U.S. President Donald Trump who has since become a vocal critic, on Friday as part of a national security probe, a source familiar with the matter said.

The investigation is focused on the potential criminal release of classified information, the source added. An FBI spokesperson confirmed "court-authorized activity" in the area of Bolton's home in the Washington suburb of Bethesda, Maryland.

The spokesperson also confirmed law enforcement activity at Bolton's Washington, D.C., office.

Bolton, who served as the U.S. ambassador to the United Nations and as White House national security adviser during Trump's first term, did not immediately respond to a request for comment. CNN reported that he said he was unaware of the law enforcement activity and was looking into it further.

Bolton has called Trump unfit for office.

The search marks the latest instance of the Trump administration moving to wield the levers of government power against Trump's perceived enemies since taking office in January.