The removal of the agent, who also had worked on the investigation of Hillary Clinton's use of a private email server, occurred this summer. The person who discussed the matter with The Associated Press was not authorized to speak about it by name and spoke on condition of anonymity.

Peter Carr, a spokesman for Mueller, said Mueller removed the agent, Peter Strzok, from the team "immediately upon learning of the allegations." He would not elaborate on the nature of the accusations.

The swift removal almost certainly reflected a desire to insulate the investigators from any claims of political bias or favoritism.