Sources: Terrorists planned plane attacks with undetectable bombs, flammable clothes

(CNN) – U.S. officials have known al Qaeda operatives in Syria, known as Khorasan, were plotting attacks since at least this spring.

But more recently intelligence suggested they were in an advanced stage of planning an attack, possibly against the U.S. using Western recruits. U.S. officials say they had to act fast to disrupt them.

CNN's Pamela Brown reports.