Clinton has said she didn't send or receive information that was classified at the time via her personal email account, which was run on a private server at her New York home. Republicans have repeatedly questioned whether her use of a private email system put sensitive information at risk.

In all, the State Department yesterday said 1,274 of Clinton's emails have been retroactively classified since the department started reviewing them for public release.

Two emails released yesterday were designated 'secret', the second-highest level of classification, which applies to information that could cause serious damage to national security if released. Most of the emails were classified 'confidential,' which is the lowest level of classification.

The messages were part of a batch of about 5,500 pages of Clinton emails released on the final day of 2015.

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