By Tabassum Zakaria and Phil Stewart
WASHINGTON (Reuters) - Despite U.S. success in weakening al Qaeda, the United States faces a long-term threat from global affiliates that are likely to exist even a decade from now, U.S. intelligence chiefs said on Tuesday.
The future of al Qaeda has been in sharp focus in the days surrounding the 10th anniversary of the September 11, 2001, attacks and since the May killing of the group's leader, Osama bin Laden, in a covert U.S. raid in Pakistan.
Bin Laden's successor, Ayman al-Zawahri, said in a video posted on Islamic websites on Tuesday that the September 11 attacks continue "to shake the pillars of the global crusade."
CIA Director David Petraeus, testifying before Congress for the first time since taking over the spy agency last week, saw vulnerability in core al Qaeda that offered a window of opportunity to further weaken the group. Petraeus also cast doubt on Zawahri's leadership abilities.
But both Petraeus and Director of National Intelligence James Clapper offered warnings about the future threat from al Qaeda's affiliates, particularly the Yemen-based al Qaeda in the Arabian Peninsula, or AQAP.
"I don't believe that al Qaeda 10 years from now will necessarily exist in the form it was today and certainly not in the form in which it was 10 years ago," Clapper said.
"What I do see though is that the so-called franchises that we talked about will probably be a threat to us."
Much of the damage against core al Qaeda has been inflicted by CIA drone strikes in Pakistan, and protesters appeared at the joint hearing of Senate and House intelligence committees with signs like "ground the drones" and "stop CIA death squads."
Petraeus said AQAP has already emerged as the "most dangerous" affiliate of the extremist group as the terrorism threat shifts to outside South Asia.
AQAP was behind the December 2009 plot to blow up a U.S. airliner as it approached Detroit and a 2010 effort to send bombs hidden in computer printers on two cargo aircraft.
Southern Somalia has become "one of the world's most significant havens for terrorists" and the al Qaeda affiliate there is large, well-funded, and has attracted hundreds of foreign fighters, including Americans, Petraeus said.
"We've achieved dramatic successes in taking down and damaging core al Qaeda but I think the whole notion of franchises or variants thereof will be with us for some time," Clapper said.
The anniversary of the September 11 attacks was accompanied by U.S. warnings about credible but uncorroborated intelligence that militants were plotting an imminent attack on the United States. But Petraeus said that intelligence remained unconfirmed.
U.S. counterterrorism and law enforcement officials said they had not completely dismissed or discredited intelligence received last week about a possible attack. It included a suggestion that Zawahri might be associated with the plot.
Zawahri voiced support in an Internet video for popular revolts shaking the Middle East. But Petraeus and Clapper said the Arab Spring revolts in Egypt, Tunisia, Libya and elsewhere weakened al Qaeda's message that violence was needed to implement change.
Petraeus said bin Laden's death in May was a "stunning blow" to the group and Zawahri is considered "less compelling as a leader" by the group's followers.
"We thus assess that he will have more difficulty than did Osama bin Laden in maintaining the group's cohesion and its collective motivation in the face of continued pressure," Petraeus said.
(Writing by Phil Stewart; Editing by Doina Chiacu)