The White House on Tuesday explicitly left open the possibility that last week's dramatic attack on the U.S. Consulate in Benghazi, Libya, which left four Americans including U.S. Ambassador Chris Stevens dead, was a planned attack.

Press secretary Jay Carney suggested the assault could have been the work of an armed group looking to "take advantage" of demonstrations he blamed on an anti-Islam video available online.

Carney repeatedly described that footage as the "precipitating" cause of the protests and the violence targeting American diplomatic posts in Egypt, Libya, Sudan, Tunisia and elsewhere.

Libya is "still a very volatile place [where] there are vast numbers of weapons, and certainly a number of violent groups in the country," he told reporters at his daily briefing.

"There is an abundance of weapons, including heavy weapons, and there are certainly groups that carry those weapons and look to take advantage of those circumstances—as there are around the region and the world," Carney said. He did not say whether such groups might be linked to international extremist networks like al-Qaida.

"We have seen circumstances in the past in other parts of the region where incidents that inflame opinion are taken advantage of, and exploited, by groups that have an interest in creating chaos and destabilizing their local governments, or attacking the West or the United States," Carney said.

Carney said he was "not aware" of any advance warning from Libyan officials regarding the assault on the American Consulate in the eastern city of Benghazi, which saw heavily armed and as-yet undisclosed fighters storm the compound and then hold it for hours against American and Libyan counterattack.

Top lawmakers briefed last week by Defense Secretary Leon Panetta emerged from the closed-door session describing the bloodshed in Benghazi as a preplanned, orchestrated attack. Secretary of State Hillary Clinton and Director of National Intelligence James Clapper are due to brief Congress on the evolving situation on Thursday. (Update: An administration official says Panetta's briefing last week was about Syria, not Libya.)

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"This is a matter that's under investigation in terms of what precipitated the attacks, what the motivations of the attackers were, what role the video played in that," Carney continued. "I am not, unlike some others, going to prejudge the outcome of an investigation and categorically assert one way or the other what the motivations are or what happened exactly until that investigation is complete."

But Carney last week repeatedly blamed the video for the violence, including the attack on the consulate in Benghazi. "It's not an assumption," he said Friday, asserting that the administration had no evidence to buttress the claim that the attack was the work of extremists. Some analysts have said it beggars belief to say that a spontaneous show of religious-themed anger would escalate into a heavily armed assault on the consulate—all on the anniversary of 9/11.

So is the White House ruling out the possibility that it was an extremist group?

"Of course not," Carney said on Tuesday. "As more information comes to light, that will obviously be a part of the investigation and we'll make it available when appropriate." When? "I don't keep FBI timelines at the ready."

He added, "Based on the information we initially had available, and have available, we do not have any indication at this point of premeditation, or preplanned attacks—but it is under investigation."

UPDATE, 9:14 p.m. ET: This post has been updated to reflect that Panetta's briefing last week as about the situation in Syria.