Intelligence sources tell Fox News they are convinced the deadly attack on the U.S. Consulate in Benghazi, Libya, was directly tied to Al Qaeda -- with a former Guantanamo detainee involved.

That revelation comes on the same day a top Obama administration official called last week's deadly assault a "terrorist attack" -- the first time the attack has been described that way by the administration after claims it had been a "spontaneous" act. 

"Yes, they were killed in the course of a terrorist attack on our embassy," Matt Olsen, director of the National Counterterrorism Center, said during a Senate hearing Wednesday. 

Olsen echoed administration colleagues in saying U.S. officials have no specific intelligence about "significant advanced planning or coordination" for the attack. 

However, his statement goes beyond White House Press Secretary Jay Carney and Susan Rice, the U.S. ambassador to the United Nations, saying the Sept. 11 attack on the consulate was spontaneous. He is the first top administration official to call the strike an act of terrorism.

Sufyan Ben Qumu is thought to have been involved and even may have led the attack, Fox News' intelligence sources said. Qumu, a Libyan, was released from the U.S. prison at Guantanamo Bay, 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 2008.