A senior aide to Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE when she served as secretary of State briefly walked out of an interview with federal investigators when an FBI official began to discuss a topic considered off-limits, The Washington Post reported on Tuesday.

Cheryl Mills, Clinton's former State Department chief of staff, and her lawyer both returned to the interview room a short time later, according to the newspaper, citing several unidentified people.

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The off-limits questions reportedly concerned the way in which emails were given to the State Department to be distributed to the public. According to the Post, Mills worried that the questions would violate the attorney-client privilege, and investigators had previously agreed not to broach the subject. It is unclear when the interview occurred.

Mills’s lawyer, Beth Wilkinson, did not immediately respond to an inquiry from The Hill about the incident.

The Tuesday afternoon report comes as the federal investigation related to Clinton’s exclusive use of a private email server throughout her time at the State Department appears to be coming to a close. Interviews of Mills and other top aides have reportedly been conducted in recent weeks, and Clinton herself is expected to answer investigators’ questions soon.

According to reports, the FBI and federal prosecutors have found little evidence of mishandled government documents that would warrant pushing ahead with a criminal case.

Still, the episode with Mills shows the process has not been entirely smooth Clinton and her top allies, who have repeatedly shrugged off concerns about the server. The Post reported that Mills was seen as a cooperative witness despite the brief walkout.

Clinton, the likely Democratic presidential nominee, has said that the setup was a mistake made out of a desire for convenience and not a desire to circumvent federal recordkeeping or transparency laws.

Of the roughly 30,000 emails from Clinton’s server released by the State Department, approximately 2,000 have been classified at some level.