A "Benghazi bombshell" report has been released by CNN, claiming that the CIA has been conducting abnormally frequent polygraph tests on its employees to ensure they do not leak any information about its Benghazi operations.

The tests have allegedly been given to anyone with knowledge of the CIA's Benghazi operations, and looks to stop anyone leaking information to anyone in Congress or to the media.

The CNN sources have remained anonymous, but have described that polygraph tests have been given to staff nearly once a month.

A CNN report has claimed that as many as 35 Americans were in the Libya U.S. Embassy in Benghazi when it was attacked last September. Of those 35, 21 are thought to have been CIA operatives, who were working in a section of the embassy called the "annex." That building, it has been claimed, was being used by the CIA, although why it was being used and what work was being conducted there remains a mystery.

The CNN sources believe that the CIA is going to great lengths to keep secret the operations that were going on there. One source told CNN: "You have no idea the amount of pressure being brought to bear on anyone with knowledge of this operation."

In the Benghazi attacks last September four Americans were killed, including U.S. ambassador to Libya, Christopher Stevens.

Since that time the White House has been criticized by various groups that it had conducted a cover-up over exactly what happened, and that it was working to keep information secret.

In May, government emails were made public that showed that former CIA director, David Petraeus, had a big influence in what information was put out to the public, and how the White House shaped its reports on the incident.

The White House and the CIA have denied that there was any cover-up.

Watch the report in the video below: