President Obama says Hillary Clinton "could not have been more diligent" as secretary of state in a video her campaign released mere hours after FBI director James Comey accused her of being "extremely careless" in her handling of classified materials during her tenure.

"She could not have been more diligent, more tireless, more loyal, and more committed to making sure that around the world, diplomatically, we were promoting the interests and goals of the American people," says Obama in the two-minute promotional spot the Clinton camp characterized as an " interview".

Earlier Tuesday, Comey announced the findings of the FBI's investigation into Clinton's use of a personal email system during her time at the State Department. While stopping short of recommending an indictment, the Bureau criticized her behavior and "the security culture of the State Department in general."

"Although we did not find clear evidence that Secretary Clinton or her colleagues intended to violate laws governing the handling of classified information, there is evidence that they were extremely careless in their handling of very sensitive, highly classified information," Comey said at a press conference.

"While not the focus of our investigation, we also developed evidence that the security culture of the State Department in general, and with respect to use of unclassified e-mail systems in particular, was generally lacking in the kind of care for classified information found elsewhere in the government."

The FBI's conclusions include:

From the group of 30,000 e-mails returned to the State Department, 110 e-mails in 52 e-mail chains have been determined by the owning agency to contain classified information at the time they were sent or received. Eight of those chains contained information that was Top Secret at the time they were sent; 36 chains contained Secret information at the time; and eight contained Confidential information, which is the lowest level of classification. Separate from those, about 2,000 additional e-mails were "up-classified" to make them Confidential; the information in those had not been classified at the time the e-mails were sent. ... [S]even e-mail chains concern matters that were classified at the Top Secret/Special Access Program level when they were sent and received. These chains involved Secretary Clinton both sending e-mails about those matters and receiving e-mails from others about the same matters. There is evidence to support a conclusion that any reasonable person in Secretary Clinton's position, or in the position of those government employees with whom she was corresponding about these matters, should have known that an unclassified system was no place for that conversation. In addition to this highly sensitive information, we also found information that was properly classified as Secret by the U.S. Intelligence Community at the time it was discussed on e-mail (that is, excluding the later "up-classified" e-mails). None of these e-mails should have been on any kind of unclassified system, but their presence is especially concerning because all of these e-mails were housed on unclassified personal servers not even supported by full-time security staff, like those found at Departments and Agencies of the U.S. Government—or even with a commercial service like Gmail.