The roughly 150 emails are among 7,000 pages of new emails from Hillary Clinton's private server that the State Department will publish on its public records website later tonight -- part of its ongoing effort to make all of 30,000 emails public.
Tonight's publication will bring the total number of emails that had to be upgraded to classified to around 213. The exact number of newly classified emails to be released tonight in redacted form is still being calculated, State Department spokesman Mark Toner said today.
Clinton has long maintained that while she was serving as secretary of state, she never handled any emails on her private server that were marked classified. State Department officials have also noted that the emails were not classified at the time they were sent, but the number of emails that were later deemed classified demonstrates that whether or not they were marked classified, the emails were sensitive in nature.
It is not possible to send a properly marked and classified email through an unclassified State Department account or a private email account, according to multiple senior government officials familiar with handling sensitive materials in the government email system.
Each of the 150 emails newly deemed classified were considered exempt from public release using a specific guideline of the Freedom of Information Act (FOIA). Specifically, the regulation states that anything deemed to contain "classified information for national defense or foreign policy" is exempt from public release.
Emails marked under this specific exemption are considered "confidential" in nature, one of the lowest levels of classification.
The Clinton campaign did not immediately respond to a request for comment from ABC News.