State Department investigators have uncovered that one of Hillary Clinton's closest aides, Huma Abedin, was overpaid by nearly $10,000 during Clinton's tenure as secretary of state, reported the Washington Post. The revelation was made public by letters of Sen. Chuck Grassley, R-Iowa, to Secretary of State John Kerry and the State Department's Office of Inspector General.

"In May 2013, the Department of State allegedly paid Ms. Abedin $33,000 for 'unused' leave, though it is unclear whether she should have been entitled to such a payment," Grassley wrote to Kerry.

Abedin improperly received taxpayer funds because she received payment while she was away from her job, despite not requesting leave, according to the Post. She never took any vacation or sick time off work during her more than four years on the job, despite having taken at least one 10-day trip to Italy, according to Grassley's letter.

Abedin reportedly formally contested the allegation and has asked for an administrative review of the State Department investigation's conclusion.

Grassley's letter asks that Kerry respond to his inquiry about payment made to Abedin by Aug. 10.