By Suzanne Kelly and Pam Benson

U.S. officials appear less certain about what happened in Benghazi, Libya, just before the attack that killed Ambassador Christopher Stevens and three other Americans last week.

"We certainly acknowledge contradictory information about whether there was a protest prior to the attack," a U.S. official told CNN on Thursday. "We're continuing to collect information and evaluate exactly what the circumstances were prior to the attack."

U.S. officials have been saying they believe, based on the intelligence, that the attack grew out of a spontaneous protest over a trailer for an anti-Muslim film that was circulating on the Internet, and there is no indication it was a planned attack. It is a contention that critics like Republican Sen. John McCain have said is hard to believe true given the extensive attack and the amount of weaponry involved.



Susan Rice, the U.S. Ambassador to the United Nations, delivered the administration's assessment on a number of Sunday talk shows.

On CBS' "Face the Nation," Rice said, "Soon after that spontaneous protest began outside of our consulate in Benghazi, we believe that it looks like extremist elements, individuals, joined in that effort with heavy weapons of the sort that are, unfortunately, readily now available in Libya post- revolution. And that it spun from there into something much, much more violent."

But conflicting information about whether there really was a protest ahead of the attack calls into question whether the attack was planned.

National Counterterrorism Center Director Matthew Olsen told a Senate committee on Wednesday that he believed the attack fit the definition of a terrorist attack. Although he maintained the evidence so far indicated the attack was not planned, he was careful in describing just what officials knew about how it transpired and who was involved.

"The best information we have now, the facts we have now indicate this was an opportunistic attack on our embassy. The attack began and evolved and escalated over several hours," said Olsen. "It appears that individuals who were certainly well armed, seized on the opportunity that was presented as the events unfolded that evening into the morning hours of September 12th."

But both Olsen and White House Press Secretary Jay Carney added a new characterization to their account. Olsen said there was nothing specific indicating "significant advanced planning" and Carney on Thursday said there was no information to suggest "a significantly preplanned attack."

"It is, I think, self-evident that what happened in Benghazi was a terrorist attack," Carney added.

A U.S. intelligence official on Thursday also seemed more cautious.

"Simply put, while everything is still under investigation, the available information suggests the protests in Cairo inspired what the attackers decided to do later that night in Benghazi," the official said. "Right now, this points to a plan that was hatched opportunistically that day. Of course, if credible new information suggests otherwise, the investigation will pursue those leads."

The source also told CNN that "the available information suggests a group of people gathered sometime before ten o'clock that night outside of the consulate. The mixture of the people involved, and who took part in the attack, is certainly going to be part of the investigation."

CNN's Arwa Damon, who has been in Benghazi this week, reports that on the night of September 11, a group of armed individuals showed up outside the consulate around 9:30 and a firefight had broken out within 30 minutes.

On Thursday, Libya's Prime Minister Mustafa Abushagur told Damon that eight people who are believed to be involved in carrying out the attack are now detained in Libya.

But he also said the evidence so far shows the attack was planned. Approximately 30 to 50 people took part and it was clearly organized, said the prime minister, but he added there was no one specific group behind the attack.