In particular, a feared cell of Al Qaeda leaders in Syria known as the Khorasan Group has been "diminished" by the U.S. military, Comey said. Comey would not speak specifically about the killing of Muhsin Fadhli, a veteran leader of the group whom the Pentagon said was killed in a drone strike. But Comey said a campaign of military airstrikes in Syria has hurt the group`s ability to operate.
Intelligence officials have been concerned that Al Qaeda`s operatives in Syria would be able recruit fighters with European and American passports for future attacks in the West. In particular, officials believe Al Qaeda bombmakers have trained to smuggle non-metallic explosives onto airplanes and traveled from Yemen to Syria to plan attacks against Western targets.
"They were a very serious threat to the United States," Comey said during an hourlong discussion about threats facing the U.S. that was moderated by CNN`s Wolf Blitzer.
Until recently, U.S. intelligence analysts believed Islamic State`s leaders were less focused on launching attacks inside the U.S. than in gaining and ruling territory in the Middle East and North Africa. But in the last several months, the group has increased its outreach over the Internet and is producing thousands of messages each month encouraging Americans to launch attacks inside the U.S.
The "sheer volume" of social media messages produced by Islamic State militants is a major concern, Comey said. English-language Twitter accounts promoting Islamic State have more than 21,000 followers, he said.
The FBI has hundreds of investigations open in all 50 states into individuals who have been receiving messages from Islamic State and who may decide to act, Comey said.
FBI investigators are still searching for what motivated 24-year-old Mohammod Youssuf Abdulazeez to kill five servicemen in Chattanooga, Tenn., last week, Comey said. A police officer and another serviceman were injured, but their wounds are not life-threatening.
Abdulazeez spent seven months in Jordan last year. Comey confirmed that the FBI has sent agents there to interview relatives and friends who might shed light on what was going through his mind when he returned to Tennessee and decided to open fire on an armed services recruiting center and a military training facility.
"We are still combing through his entire life," Comey said.
FBI Special Agent Ed Reinhold told reporters Wednesday that Abdulazeez appeared to have been a “homegrown violent extremist” operating on his own. Days before the shooting, Abdulazeez wrote online that his life felt like a prison, and he praised disciples of the prophet Muhammad for waging jihad to establish Islam.
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