The State Department will be denying in full seven email chains found in 22 documents, representing 37 pages. "These documents were not marked classified at the time they were sent," the State Department Spokesman John Kirby said.

He added that the department was now investigating whether the information in them was classified at the time it passed through her private email account run on a server in her home.

Further, Kirby said another 18 emails which comprised of eight distinct email chains between Clinton and US President Barack Obama, are also being withheld in full from the State Department's release of documents.

"They are entirely separate and distinct from the emails in today's release that were upgraded to top secret, secret, or confidential, and I'm not going to speak again to the content of that email traffic," Kirby said.

The announcement came three days before the Iowa caucuses, when the first votes are cast for the presidential nominations. The Clinton campaign demanded that all of her emails be released by the State Department.

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