"After learning of the federal investigation, it was discovered that an individual had recently acted improperly. In the spirit of transparency and cooperation, this behavior was immediately and proactively reported to investigators. The Mayor has been and remains committed to cooperating in this matter," his attorney Boyd Johnson said in a statement.

"On Monday night, the FBI approached the mayor after an event. The Mayor immediately complied with the FBI's request and provided them with electronic devices. The mayor has not been accused of any wrongdoing and continues to cooperate with the investigation."

Mr. Adams also denied any wrongdoing in a statement.

"As a former member of law enforcement, I expect all members of my staff to follow the law and fully cooperate with any sort of investigation—and I will continue to do exactly that. I have nothing to hide," he stated.