The attack on the U.S. Consulate in Benghazi, Libya, last week appeared to be a joint operation orchestrated by an Al Qaeda affiliate in North Africa and the Islamist militia Ansar Al-Sharia, an intelligence source told Fox News, citing evidence collected so far in the investigation.
About 100 attackers carried out the "coordinated assault,” intelligence sources said, further discrediting earlier Obama administration claims that the deadly attack was a "spontaneous" outburst in response to an anti-Islam film.
Fox News' sources say the attack came in two waves and involved rocket-propelled grenades, as well as mortar fire, and both the consulate and safe house were attacked seemingly with inside knowledge.
Ansar Al-Sharia is not directly affiliated with Al Qaeda, but has sympathetic goals. Ansar has tried and failed to establish an Islamic state in eastern Libya. The militia is a name adopted by a handful of groups, including Al Qaeda in the Arabian Peninsula.
A senior Arab government official told Fox News in December 2011 that it was an effort to “rebrand” because the Al Qaeda name had so much baggage.
Libyan officials are now "absolutely convinced" the attack was preplanned, sources say, adding to recent indications that Al Qaeda was involved, specifically a former Guantanamo detainee named Sufyan Ben Qumu.
Four Americans, including U.S. Ambassador Chris Stevens, were killed in the strike, which occurred on the 11th anniversary of the Sept. 11 terrorist attacks.
White House Press Secretary Jay Carney and Susan Rice, the U.S. ambassador to the United Nations, initially described the attack on the consulate as spontaneous with little evidence of a well-planned assault. Administration officials also pointed to the anti-Islam film that has fueled protests in the Mideast against the United States, suggesting the consulate attack may have begun as one of those protests and escalated.
But this week, the administration began shifting its explanations for the attack, with National Counterterrorism Center Director Matt Olsen testifying before the Senate on Wednesday that it was a "terrorist attack."
Carney followed up by saying for the first time Thursday that it was "self evident" that the attack was an act of terrorism, but President Obama seemed to backtrack a bit when pressed later that day by a TV interviewer. Obama did not reference terrorism, instead invoking the controversial film, which some analysts have said is being used as a tool of extremists to incite violence.
Qumu, the former Guantanamo Bay detainee, is a Libyan who was released from the U.S. prison in Cuba in 2007 and transferred into Libyan custody on the condition he be kept in jail.
He was released by the Qaddafi regime as part of its reconciliation effort with Islamists in 2010.
His Guantanamo files also show he has ties to the financiers behind the Sept. 11 terrorist attacks. The declassified files also point to ties with the Libyan Islamic Fighting Group, a known Al Qaeda affiliate.
Fox News' Bret Baier, Catherine Herridge and Pamela Browne contributed to this report.