US State Department to reopen Clinton emails probe

"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.

The FBI advised earlier in the week that no charges be brought over Clinton's use of a private email account and homebrew server during her time as secretary of state from 2009 to 2013, a recommendation that the Justice Department then followed.

Although the announcement took a huge weight off the presumptive Democratic nominee, FBI chief James Comey nonetheless said Clinton and her staff were "extremely careless in their handling of very sensitive, highly classified information."

Republicans, including Clinton's White House rival Donald Trump, have cried foul over the lack of charges, alleging that Clinton's influence as a prominent politician helped her escape criminal proceedings.

Trump, who polls show faces an uphill battle against Clinton in November, has repeatedly accused Clinton of masking her involvement in illegal activity by deleting more than 30,000 emails she claimed were personal and not related to her job as top US diplomat.

On Thursday, Comey was forced to vigorously defend his recommendation before the House Committee on Oversight, which summoned him to testify.

Despite tense moments, Comey, a Republican former prosecutor, maintained his cool throughout the marathon grilling that lasted four hours and 40 minutes.

Although Kirby declined to provide specific information about the State Department's latest review, he said it would aim to be "as transparent as possible about our results, while complying with our various legal obligations."

Of some 30,000 emails Clinton turned over to the FBI, Comey said 110 contained classified information -- Clinton had said none was classified at the time they were sent.