The US State Department said Thursday that it would reopen its internal investigation of whether Democratic White House hopeful Hillary Clinton's use of a private email account and server compromised her handling of classified material.

"We will aim to be as expeditious as possible, but we will not put artificial deadlines on the process," department spokesman John Kirby said, noting that the internal review could proceed now that the Justice Department investigation wrapped up with no charges filed against the former secretary of state.