Classified emails stored on former Secretary of State Hillary Clinton’s private server contained information from multiple intelligence agencies in addition to data connected to the 2012 Benghazi attack, a source familiar with the investigation told Fox News.

The information came from the National Security Agency, the Defense Intelligence Agency, the National-Geospatial Agency, as well as the Office of the Director of National Intelligence and the Central Intelligence Agency, the source said.      

A random sampling of emails by the Office of the Intelligence Community Inspector General has identified five emails containing classified information. One of the classified emails was released in full by the State Department on its “reading room” public website for Clinton’s emails. 

The details about classified and sensitive material have put increasing pressure on Clinton in recent days to turn over her server for inspection. It was revealed last week that intelligence community and State Department watchdogs warned potentially "hundreds" of classified emails were on the system. Clinton has said all along she never sent or received information that was classified at the time. 

The official responsible for overseeing the government’s security classification system, John Fitzpatrick, told McClatchy Newspapers that while reviewing four years of Clinton’s emails, intelligence agencies grew concerned that State Department officials were not guarding classified information in screening documents for public release.

A congressional source told Fox News that in early July, Patrick Kennedy, the State Department’s undersecretary for management, met with about a dozen staffers on Capitol Hill from the intelligence, homeland security and foreign affairs committees.

In the meeting, Kennedy made the argument that he had checked with CIA and the publicly released email had no classified information, but that the agency was not the originating agency for the intelligence and would have no say over the classification issue, the source said.   

Staffers however questioned why the meeting was held in a classified setting, the source told Fox News, adding that Kennedy carried the email with him in a locked black bag, reserved for classified information.

A CIA spokesperson had no public comment on Thursday to Fox News, while the ODNI referred calls to the inspector general of the intelligence community.

Fox News’ Catherine Herridge contributed to this report.