Until now, none of the released emails were marked as classified, despite 1000 of them had lower classification levels.

Also, another source, who spoke on condition of anonymity, has backed up the finding, which shows the emails include intelligence from "special access programs", or SAP, that is deemed to be beyond "Top Secret".

She said the emails were not classified as secret at the time and should all now be released, adding: "Let the public see them".

We understandthat these e-mails likely originated on the State Department's unclassified system before they wereever shared with secretary Clinton, and they have remained onthe department's unclassifiedsystem for years.

Those questions, he said, "are being, and will be, handled separately by the State Department", indicating that the State Department is looking into Mrs. Clinton's claim that she "never sent or received any e-mail that was deemed classified, that was marked classified".

Clinton campaign managers, meanwhile, slammed the State Department's decision and said it is "over-classification run amok".

Hillary Clinton insisted Monday there is "nothing new" on the email controversy hanging over her campaign, saying yet again that she wants all of her emails released by the State Department.

The State Department on Friday refused to make public 22 emails from Clinton's server marked "top secret". We feel no differently today.” Fallon accused the “loudest and leakiest participants” in a process of bureaucratic infighting for withholding the exchanges.

Mrs Clinton's use of a personal email as secretary of state has dogged her bid for the USA presidency. The Federal Bureau of Intelligence is trying to find out whether the material involved was mishandled.

Spokesman John Kirby said the emails, which he described as "22 documents covering 37 pages", would therefore not be released publicly along with other emails from the Democratic White House candidate's controversial archive.

Kirby also disclosed today that the State Department is withholding eighteen emails between Hillary Clinton and President Obama, but not because they were determined to be classified. But it is the responsibility of individual government officials to handle classified material appropriately, including by properly marking it as classified, according to experts.

Hillary should have had the discernment, wisdom and just plain common sense not to put the country's intelligence secrets at risk by using a private server for her work-related emails. Should Bernie Sanders go on the attack instead of supporting Clinton on this issue?

Friday was supposed to be the deadline for releasing all of the 33,000 emails from the server, but officials have appealed for an extension of the deadline.

Beyond this, though, there is something downright unseemly about the media's determination to have this issue become a major factor in the Democratic primary process.

At the time, several officials from different agencies suggested the disagreement over the drone emails reflected a tendency to overclassify material and a lack of consistent classification policies across government.

Since this was during Clinton's tenure as secretary of state, and considering that she had signed two separate non-disclosure agreements, her claims of innocence based on ignorance ring a little hollow.

Legal questions aside, it's the potential political costs that probably more concern Clinton. A spokesman, Brian Fallon, said that all of the emails should be released.