Washington (CNN) -- Al Qaeda is weakened but remains a significant threat to the United States, the nation's top intelligence officials told a congressional committee Tuesday.
CIA Director David Petraeus, the former military commander in Afghanistan who made his first congressional appearance as a civilian at the rare joint hearing by the intelligence committees of the House and Senate, said al Qaeda is far weaker today than it was 10 years ago, at the time of the 9/11 attacks, because of the killing of Osama bin Laden and other successful attacks on leaders in Pakistan and Afghanistan.
According to Petraeus, the "heavy losses to al Qaeda senior leadership appear to have created an important window of vulnerability for the core al Qaeda in Pakistan and Afghanistan," and the United States will need a "sustained focused effort" to exploit the opportunity.
Petraeus called bin Laden's long-time deputy and successor, Ayman al-Zawahiri, a "less compelling" leader who will have more difficulty that bin Laden "in maintaining the group's cohesion and its collective motivation in the face of continued pressure."
"Some mid-level leaders and rank-and-file al Qaeda members may increasingly seek safe haven across the border in Afghanistan or decide to leave South Asia," Petraeus said, adding that "even in decline, with its core leadership having sustained significant losses, al Qaeda and its affiliates still pose a very real threat that will require" continued U.S. focus and dedication "for quite a while."
He called al Qaeda in the Arabian Peninsula, a Yemen-based affiliate, the most dangerous of al Qaeda's various "nodes," citing the group's two nearly successful attacks on the United States: the December 2009 attempt to blow up a Northwest airliner as it approached Detroit and the cargo bomb plot of 2010.
Petraeus labeled Somalia "one of the world's most significant havens for terrorists," saying Al-Shabaab, the al Qaeda affiliate there, is large and well-financed and is training hundreds of foreign fighters, including some Americans.
Director of National Intelligence James Clapper, who also took part in the hearing, agreed that despite U.S. successes against it, al Qaeda remains a threat. He pointed to the terror concerns over this past weekend regarding a possible plot timed to the anniversary of the 9/11 attacks.
"Terrorists still wish to do us harm, to destroy our institutions and to kill Americans without conscience," he said.