The U.S. State Department said Monday that 305 emails need to be further reviewed for potentially classified information from Hillary Clinton's email archives handed over by the former top U.S. diplomat last year.

After reviews by the country's five intelligence agencies, a total of 305 emails, or about 5 percent of the emails so far reviewed, may have contained classified information and need to be reviewed further, the federal agency said in a court filing.

"Out of a sample of approximately 20 percent of the Clinton emails, the reviewers have only recommended 305 documents -- approximately 5.1 percent -- for referral to their agencies for consultation," the State Department court filing said.

Monday's filing was part of a Freedom of Information Act lawsuit by a U.S. journalist who sought access to Clinton's email records.

The revelation of Clinton's exclusive use of her personal email account and a private email server while helming the State Department from 2009 to 2013 came under fierce attacks from her Republican rivals as the former secretary of state was launching her second bid to win the White House. ( In a press conference in March, Clinton said she had exchanged about 60,000 emails during her stint in the Obama administration, among which about half were personal and thus deleted. The Clinton camp turned over the other half, 30,000 emails in total, to the State Department.

The State Department is currently reviewing and releasing Clinton's emails on a monthly basis, and after the U.S. intelligence community raised concerns that a classified document was included in an earlier release of a batch of Clinton emails, a team of reviewers from five U.S. intelligence agencies joined the State Department to review the emails in mid-July.

Clinton had stressed repeatedly that she did not exchange any classified information via her personal email account.

While the setup of the federal emailing system makes it impossible to forward an email marked as "classified" to a private account, it is still possible to paraphrase or retype classified information and send it as an unprotected message to a personal account.

The controversy surrounding Clinton's propensity to be overprotective regarding her emails threatens to obstruct Clinton's otherwise smooth path to the Democratic nomination as an increasing number of voters have begun to see her as untrustworthy.

Clinton relented last week and handed over the private server to the Justice Department for review in a move to seek an end to an issue that has so far proved a major distraction to her campaign.