WASHINGTON — The State Department has withdrawn Hillary Clinton's security clearance at her request amid an ongoing review at the agency of the former secretary of state and her private email server.

A letter dated Sept. 21 to the leadership of the Senate Judiciary Committee, and published Friday by Republican Sen. Chuck Grassley, states that Clinton's clearance was withdrawn on Aug. 30. It doesn't explain why Clinton requested the measure, but her clearance was pulled just days after President Donald Trump revoked the clearance of former CIA Director John Brennan.

Trump also publicly threatened to revoke the clearances of other Obama-era officials, though Clinton was not on his list.

The letter also lists five Clinton aides whose security clearances were withdrawn in September. The names of the aides were redacted, except for Cheryl Mills, who served as Clinton's chief of staff at the State Department.

The State Department noted to Grassley and Sen. Dianne Feinstein, the top Democrat on the judiciary committee, that it was still examining all of the documents it received from the FBI after the bureau's investigation was completed.

After its review is complete the State Department said it will begin investigating whether there were any "valid security incidents" and whether Clinton or her staff broke any rules.

Clinton was investigated over her use of a private email server during her run for president against Trump. She used the email for business while she was secretary and handled classified information. The FBI closed its investigation and did not charge Clinton.