What is Khorasan?

The battlefield in Syria's civil war is carved up among several large groups ostensibly trying to oust President Bashar Assad, but spending a great deal of time instead fighting each other for territorial gains.

That focus on their immediate surroundings has thus far, according to most U.S. officials, helped to mitigate the threat posed by groups like the Islamic State of Iraq and Syria (ISIS) to the U.S. homeland.

There has been significant and mounting concern that Western recruits drawn into the war -- who have proven all but impossible to monitor on Syrian soil -- could use their passports to sneak back into the U.S. or Europe and stage attacks.

Now, however, a previously unheard of subgroup within the complicated jihadist web that is the Syrian opposition is lending new urgency to that concern by combining the threat of Western imports with the threat of advanced bomb-making.

Former CIA deputy director Mike Morell explained on "CBS This Morning" that a group of militants from al Qaeda-central, near Pakistan's border with Afghanistan, have joined the fight in Syria and "evolved into the external operations arm" of the group's franchise in that country, the al-Nusra Front.

"Khorasan members came from Pakistan," said Morell. "They focus on attacks in the West."

Specifically, as reported by CBS News' Bob Orr, the Khorasan group is focused on trying to build bombs capable of being sneaked onto airliners, and finding the Western jihadists in Syria who could try and carry them.

As for why al Qaeda has deployed a group to try and recreate in some fashion their Sept. 11 plot, Morell said the group sees the aviation industry "as a symbol of the West."

In addition, "they believe if they damage the airlines they can damage the American economy, as we saw with 9/11," Morell said, adding that the terror network is also likely still of the mind that what worked once can work again.

What makes Khorasan so dangerous -- given its presumed access to the pool of hundreds of U.S. and European jihadists who have flooded into Syria to join the fight -- is the group's suspected members from or trained by al Qaeda's branch in Yemen, AQAP.

AQAP has been considered for years one of the most direct and imminent threats to the U.S., boasting al Qaeda's master bomb-builder, Ibrahim al-Asiri.

"That is very worrisome because that brings together two pieces of a potential plot in the West," said Morell. "It brings together Western fighters who have gone to Syria to fight -- so capable of carrying out operations in the West -- with this bomb technology that Asiri brings to the table. You put those things together, you have a serious threat."