Updated

Within eight hours of the initial attack on the United States' diplomatic facility in Benghazi, Libya, the CIA decided to scrub and abandon rather than protect its annex, a military intelligence source told Fox News.

“The defensive posture was no longer sustainable," the source told Fox News, revealing for the first time how quickly the CIA chose to secure classified material and close down the facility after it took indirect fire from two mortars at about 5:15 a.m. local time Sept. 12.

The adjoining U.S. consulate, by contrast, has never been secured, even three months after the attack.

The process to sanitize the CIA site began on Sept. 11 after the consulate was attacked around 9:35 p.m. local time. The initial stages of the agency’s proscribed evacuation plan kicked in as a precautionary step.

Given the CIA Annex was designated a high-threat posting by the agency and described to Fox News as having an “expeditionary” feel, there was not a lot of classified material to dispose of. Classified communications equipment was also near minimum.

Within two and a half hours of the decision by the CIA chief of base, the agency’s point person in Benghazi, the annex was cleared of all classified material and equipment. Both CIA Director David Petraeus and Director of National Intelligence James Clapper, who oversees the nation’s 16 intelligence agencies, were notified of the decision, which was made on the ground in Libya and not directed by Washington.

Fox News has previously reported, based on conversations with current and former intelligence officials, that there is significant evidence the terrorist attack in Benghazi was designed to flush out any remaining Western influence in eastern Libya, and specifically the growing CIA presence.

The Benghazi consulate, where Ambassador Christopher Stevens and Foreign Service Officer Sean Smith were killed, was never secured in the same way. As recently as Nov. 1, six weeks after the terrorist attack and nearly a month after an FBI team briefly collected evidence there, Foreign Policy magazine reported its journalists had found sensitive documents at the consulate, which included unsent memos about “troubling” surveillance by Libyan security guards.

While not commenting on the record, citing the sensitive nature of the information, two congressional sources told Fox News the timeline on the annex shutdown shows that the public exposure of the depth and breadth of the CIA operation in Benghazi was of significant concern to the U.S. intelligence community.

Asked for a response, a CIA spokesperson declined, saying the agency does not comment on operational matters.