SEEN: ISIS building capacity for mass casualty attacks

Washington (CNN) - Some in the U.S. intelligence community warn that ISIS may be working to build the capability to carry out mass casualty attacks, a significant departure from the terror group's current focus on encouraging lone wolf attacks, a senior U.S. intelligence official told CNN on Friday.

To date, the intelligence view has been that ISIS is focused on less ambitious attacks, involving one or a small group of attackers armed with simple weapons. In contrast, al Qaeda in the Arabian Peninsula, or AQAP, has been viewed as both more focused on -- and more capable of -- mass casualty attacks, such as plots on commercial aviation. Now the intelligence community is divided.

Meanwhile, the U.S. effort to train rebels in Syria to fight ISIS is having trouble. The few rebels that the U.S. has put through training are already in disarray, with defense officials telling CNN that up to half are missing, having deserted soon after training or having been captured after last week's attack by the al-Qaeda-affiliated Nusra Front attack on a rebel site.

One defense official admitted to CNN that "they are no longer a coherent military unit," and Pentagon officials acknowledged the approach of how to support the rebels has to change.

The potential change within ISIS itself is driven -- in part -- by a broadening competition between ISIS and AQAP for attention and recruits.

That same competition was evident this week when AQAP bomb-maker Ibrahim al-Asiri made an online appeal to supporters to carry out lone wolf attacks.

"I think they're taking a lot of the new recruits that don't have time to train, who have not been brought up in their systems, and they're using them to create the type of mass casualty which produces the media attention, which is exactly what they want, that shows they're still powerful," said CNN Military analysts Lt. Gen. Mark Hertling. Meanwhile, ISIS is continuing to draw large numbers of new foreign recruits. U.S. intelligence assesses that the formidable flow of foreign fighters to Syria and Iraq has not abated.

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