U.S. intelligence officials knew within 24 hours of the assault on the U.S. Consulate in Libya that it was a terrorist attack and suspected Al Qaeda-tied elements were involved, sources told Fox News -- though it took the administration a week to acknowledge it.

The account sharply conflicts with claims on the Sunday after the attack by U.S. Ambassador to the United Nations Susan Rice that the administration believed the strike was a "spontaneous" event triggered by protests in Egypt over an anti-Islam film.

Intelligence sources said that the Obama administration internally labeled the attack terrorism from the first day in order to unlock and mobilize certain resources to respond, and that officials were looking for one specific suspect. The sources said the intelligence community knew by Sept. 12 that the militant Ansar al-Shariah and Al Qaeda in the Islamic Maghreb were likely behind the strike.

Further, an official said, "No one ... believed that the mortars, indirect and direct fire, and the RPGs were just the work of a mob -- no one."

Yet a congressional source told Fox News that CIA Director David Petraeus, during a briefing with members of the House Intelligence Committee three days after the attack, espoused the view that Benghazi was an out-of-control demonstration prompted by the YouTube video. According to the source, this was "shocking" to some members who were present and saw the same intelligence pointing toward a terrorist attack.

In addition, sources confirm that FBI agents have not yet arrived in Benghazi in the aftermath of the attack. Four Americans, including U.S. Ambassador Christopher Stevens, were killed in the assault.

The claims that officials initially classified the attack as terrorism is sure to raise serious questions among lawmakers who from the beginning have challenged the narrative the administration put out in the week following the strike. A few Republican lawmakers have gone so far as to suggest the administration withheld key facts about the assault for political reasons.

"I think we should have answers right away. ... I think they're reluctant to tell us what this event really was probably because it's an election year. But the American people deserve to know answers about what happened at our embassy in Libya," Sen. Kelly Ayotte, R-N.H., told Fox News.

One intelligence official clarified to Fox News that there was not a "definitive" lead on who might have been responsible for the Libya attacks in the immediate aftermath, though officials had an idea of the suspects.

"It's inaccurate to suggest that within the first 24 hours there was a definitive calling card and home address for the perpetrators of the Benghazi attack. Potential suspects and data points emerge early on, but it still takes time to be certain who is responsible," the official said.

Curiously, Obama referred to "acts of terror" in his first public remarks about the attack. But from there, administration officials went on to blame the anti-Islam film.

Rice was the most explicit in that explanation, insisting on a slew of Sunday shows that the attack was not pre-planned and was tied to the film.

Obama still has not publicly and specifically described the Benghazi attack as terrorism.

But top administration officials have gradually walked back Rice's version of events.

Secretary of State Hillary Clinton reportedly suggested Wednesday to foreign leaders visiting the United Nations summit in New York that the Al Qaeda affiliate in North Africa was involved.

"Now with a larger safe haven and increased freedom to maneuver, terrorists are seeking to extend their reach and their networks in multiple directions," Clinton told the group, according to The New York Times. "And they are working with other violent extremists to undermine the democratic transitions under way in North Africa, as we tragically saw in Benghazi."

She was referring to Al Qaeda in the Islamic Maghreb.

Clinton earlier this week called the attack terrorism, two weeks after the fact. White House Press Secretary Jay Carney also said that Obama now believes it is terrorism as well.

Fox News' Bret Baier and Catherine Herridge contributed to this report.