The officials declined to be identified because of the sensitive intelligence matters involved.

Defense Secretary Leon Panetta said Thursday that AQIM was responsible for the attack, but offered no details how the United States reached that conclusion. Panetta was also critical of Algerian cooperation.

"I have to tell you, we still, as of this moment, have not been able to look at the specifics of who was involved, who took -- who took place. We understand the Algerians are questioning two individuals that they were able to capture during this operation. So we're hoping that we'll get better information from them specifically as to who was involved," Panetta said.

Extremist groups in North Africa have fluid affiliations, and members may be associated with different groups. That loose nature makes it difficult to pinpoint culpability after attacks like that in Algeria and on the U.S. consulate there in Benghazi.

General Martin Dempsey, chairman of the Joint Chiefs of Staff, underscored the concern about diverse al Qaeda elements in North Africa.

"The way to think about North Africa and West Africa is (as) a syndicate of groups who come together episodically, when it's convenient to them, in order to advance their cause. Sometimes their cause is terrorism. Sometimes it's criminal. Sometimes it's arms trafficking," he said.

Dempsey described what he called "connective tissue" between the al Qaeda groups - saying "they work together when it's convenient to them. And what we have to be alert to is that."

Panetta renewed a vow to go after perpetrators of both the Algerian attack and the one on the U.S. compound in Benghazi.

"If we find out who the perpetrators were, we're going to go after them," Panetta said. "And so that's -- you know, that will be the first challenge, is to determine precisely who was involved here. Americans were killed, and we don't stand by when Americans are killed and not take action."

Panetta would not say whether he thought action would come from the U.S. military or the FBI.