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.