A State Department spokesman refused to answer questions Monday about why the Department of Homeland Security was never alerted to the existence of Hillary Clinton's private server.

"I don't have any information on that today," said John Kirby, State Department spokesman. "Some of these issues are under review and under investigation, and there may be a real limit here on what we can do in terms of detail on that."

Each federal agency has been required to submit a list of all systems to DHS every 30 days since 2010, but the State Department never disclosed Clinton's server, according to a report by Fox News.

The submissions, made through the "Continuous Diagnostics and Mitigation" program, were intended to allow DHS to identify weaknesses in the government's cybersecurity.

But DHS was never able to audit the security of Clinton's server because the agency was never notified of its existence.

The server was used by Clinton exclusively for her government communications, and by at least one of her aides for a portion of their official correspondence.

FBI investigators are now looking into whether Clinton and her staff mishandled the classified information that resided on the server, which is presently in Justice Department custody.

The lack of a DHS audit emerged from a Freedom of Information Act request filed by Fox in June.