State Department

In July, State Department officials installed a safe at the office of attorney David Kendall after the government determined some of Clinton's emails may have contained classified information. But it said last week the safe wasn't suitable for so-called top secret, sensitive compartmented information, known as TS/SCI, which the government has said was found in some messages.

In an interview with The Associated Press during a Labor Day campaign swing through Iowa, the front-runner for the Democratic presidential nomination also said the lingering questions about her email practices while serving as President Barack Obama's first secretary of state have not damaged her campaign.

In a filing Monday as part of a lawsuit against the State Department, officials told a U.S. District Court judge in Washington they would be able to meet an existing schedule to release copies of Clinton's emails because only about 5 percent of the messages reviewed so far contain possible secret information. 

The agency said those 305 emails with potential classified data were among more than 1,500 documents analyzed so far.

The information reached the Associated Press through U.S. officials who have reviewed the correspondence.

The sourcing of the information in the emails could have significant political implications as the 2016 presidential campaign heats up.