WASHINGTON (AP) — A veteran FBI counterintelligence agent was removed from special counsel Robert Mueller’s team investigating Russian election meddling after the discovery of an exchange of anti-Trump text messages, a person familiar with the matter said Saturday.

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 publicly 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.”

The decision was likely in keeping with the Justice Department’s desire to insulate the investigators from claims of political bias or favoritism. President Donald Trump and many of his supporters have sought to discredit the investigation, in part by claiming a close relationship between Mueller and fired FBI Director James Comey and by pointing to political contributions to Democratic candidates made by some lawyers on the team.

So far, four people have been charged as a result of Mueller’s investigation. The most recent charge occurred Friday when former national security adviser Michael Flynn pleaded guilty to lying to the FBI.

The nature of the messages Strzok exchanged and with whom he communicated was not immediately clear. The Justice Department’s inspector general is investigating the matter.

The New York Times first reported the agent’s removal. The FBI declined to comment.

Strzok was present during Clinton’s July 2016 interview with the FBI about her use of a private email server while she was secretary of state, according to an unclassified summary of the interview commonly referred to as an FBI 302 form. Several other FBI agents and officials from the Justice Department also attended.

On Saturday, the Justice Department’s inspector general’s office released a statement confirming that it was continuing to review unspecified allegations made about the department’s and the FBI’s actions “in advance of the 2016 election.”

“The OIG has been reviewing allegations involving communications between certain individuals, and will report its findings regarding those allegations promptly upon completion of the review of them,” the inspector general’s office said.

The statement didn’t refer to any agents or officials by name.

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Associated Press writer Chad Day contributed to this report.