Washington (CNN) -- Al Qaeda in the Arabian Peninsula is "a significant threat to the homeland" despite the death of U.S.-born cleric Anwar al-Awlaki, who was killed last week in Yemen by a U.S. drone strike, FBI Director Robert Mueller said Thursday.
Al-Awlaki was "behind the recruiting of personnel who could undertake attacks in the United States," Mueller said.
He said the organization, commonly referred to as AQAP, still has the ability to make improvised explosive devices, although it would be "somewhat more difficult" for the group to find operatives to bring them into the United States on airplanes. But the FBI chief said the possibility of finding such people still exists.
That view was echoed by the head of the National Counterterrorism Center, Matthew Olsen, who joined Mueller for testimony before the House Intelligence Committee.
"We remain concerned about the group's intent to attack Western targets as well as its propaganda efforts designed to inspire like-minded Western extremists," Olsen said.
President Barack Obama and other officials have described al-Awlaki as the terror group's leader of external operations and said he was focused on attacking the United States. Having lived in the United States, he was considered a potent recruiter of American extremists.
But according to Olsen, the deaths of al-Awlaki -- who died along with another U.S. citizen, AQAP propagandist Samir Khan -- may not be enough to cripple the group's recruiting efforts. "We are monitoring how the loss of Awlaki and Khan will affect AQAP's propaganda machine," Olsen said.
According to an FBI and Department of Homeland Security joint intelligence bulletin issued shortly after al-Awlaki was killed, he allegedly "provided instructions on detonating an explosive device" to Umar Farouk AbdulMutallab, who is accused of trying to ignite a bomb hidden in his underwear while aboard a Detroit-bound plane on Christmas Day of 2009.
That law enforcement document also says al-Awlaki "directed" the failed 2010 plot to blow up cargo planes with explosives hidden in printer cartridges.
U.S. officials say Ibrahim Hasan al-Asiri, the bomb-maker who allegedly designed those devices, is still at large in Yemen.