The Obama Administration now believes the attack and hostage-taking at a natural gas plant in Algeria last week is the work of al Qaeda operatives based out of northern Mali.
U.S. officials say al Qaeda in the Islamic Maghreb (AQIM) was behind the attack and may also have operated a communications network from northern Mali. Despite the recent French intervention, large areas of Mali remain in the hands of jihadist groups.
One senior U.S. official said "elements of AQIM" may have carried out the offensive in tandem with fighters loyal to Moktar Belmoktar, a veteran militant based in northern Mali who has claimed responsibility for the assault.
Last year, Belmoktar was said to have been demoted by the Emir of AQIM, Abdel Malek Droukdel, but is thought to have retained links to the organization.
One U.S. official told CNN that American intelligence gatherers are trying to determine if the two factions had reunited for the attack. If so, that would indicate greater communications among North African elements of al Qaeda affiliates and splinter groups than previously thought.
U.S. intelligence believes some of the attackers came into Algeria from training camps in Libya, whose border is about 40 miles (60 kilometers) from the In Amenas site.
One of the officials emphasized that the United States is now relying on intelligence it has gathered "by other means" because of the lack of information coming from the Algerian government. It has long been privately acknowledged that the U.S. intelligence community has the ability to gather imagery and intercept communications using a variety of military and CIA platforms such as satellites and aircraft.
"We have other ways of assessing who the perpetrators were," he said, but warned the information on Mali could change as more information emerges.
That official said that intelligence gathered so far indicates "this was a relatively sophisticated attack."
"It took planning to select and case the facility, and coordinate to attack it. They had to penetrate the perimeter security and take hostages. That doesn't just happen," he said.
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.
The senior official said the United States still hopes governments in the region will take the lead, but acknowledged that seems unlikely where central governments are weak.
These assessments come as the top U.S. commander for Africa told a Washington audience that "our highest priority is countering a growing network of extremist organizations in Africa."
General Carter Ham, commanding general of U.S. Africa Command, said Thursday he sees "synchronization" of terror operations across Africa, including more collaboration, closer ideology, and the sharing of funds, weapons and explosives.
Ham expressed doubt that al Qaeda in Mali could be defeated.
"Realistically, we would all like to see the elimination of al Qaeda and others from northern Mali. Realistically, probably the best you can get is containment and disruption so that al Qaeda is no longer able to control territory as they do today," Ham said.