WASHINGTON — Saying they obtained new evidence, senior White House officials said Sunday that the Pakistani Taliban were behind the failed Times Square bombing.
The attempt marks the first time the group has been able to launch an attack on U.S. soil.
While U.S. officials have downplayed the threat — citing the bomb's lack of sophistication — the incident in Times Square and the Christmas Day airline bomber indicate growing strength by overseas terrorist groups linked to al-Qaida even as the CIA says their operations are seriously degraded.
The finding also raises new questions about the U.S. relationship with Pakistan, which is widely known to have al-Qaida and other terrorist groups operating within its borders.
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Concerning the Pakistani Taliban, Attorney General Eric Holder said: "We know that they helped facilitate it; we know that they helped direct it. And I suspect that we are going to come up with evidence which shows that they helped to finance it. They were intimately involved in this plot."
John Brennan, the president's homeland security and counterterrorism adviser, made similar remarks, linking the bomber to the Tehrik-e-Taliban Pakistan, or TTP.
Neither official said what the new evidence was.
Faisal Shahzad, a U.S. citizen of Pakistani descent, is believed to have spent five months in Pakistan before returning to the United States in February and preparing his attack.
Shahzad has told investigators that he trained in the lawless tribal areas of Waziristan, where both al-Qaida and the Pakistani Taliban operate. He was arrested aboard an Emirates Airlines jet in New York minutes before it was scheduled to take off for Dubai.
After the attack, U.S. officials said they were exploring potential links to terrorist groups overseas but said it was likely that Shahzad was acting alone and that it was an isolated incident.
Last week, Homeland Security Secretary Janet Napolitano, told NBC News that "at this point I have no information that it's anything other than a one-off." Gen. David Petraeus told the Associated Press that Shahzad apparently operated as a "lone wolf."
Brennan on Sunday rejected suggestions that that the attempted bombing shows that terrorist groups overseas were gaining strength.
"They now are relegated to trying to do these unsophisticated attacks, showing that they have inept capabilities in training," he said.
The link between an attack on U.S. soil and terrorist groups operating inside Pakistan opens up a new chapter in relations between the two countries. Until recently, administration officials have said they thought Islamabad was doing all it could.
Secretary of State Hillary Rodham Clinton said Washington expects more cooperation from Pakistan in fighting terrorism and warned of "severe consequences" if an attack on U.S. soil were successful and traced back to the South Asian country.
Brennan said Islamabad was being cooperative in the investigation but that the U.S. wants to know exactly who may have been helping Shahzad.
"There are a number of terrorist and militant groups operating in Pakistan," he said. "And we need to make sure there's no support being given to them by the Pakistani government."
Pakistani army spokesman Maj. Gen. Athar Abbas, who last week said he doubted the Pakistani Taliban had anything to do with the failed bombing, declined to comment Sunday. He said representatives of the country's civilian government should respond. They were not available for comment.
Brennan would not say whether Shahzad may be connected to fugitive al-Qaida cleric Anwar al-Awlaki, other than to acknowledge his Internet sermons are popular among extremist Muslims.
Defense Secretary Robert Gates said Pakistan has recently stepped up efforts to root out extremist militants.
"The Pakistanis have been doing so much more than 18 months or two years ago any of us would have expected," Gates told reporters at Fort Leavenworth, Kan., this week.
He referred to Pakistani Army offensives, dating to spring 2009, against Taliban extremists in areas near the Afghan border, including in south Waziristan.
Gates said the Obama administration is sticking to its policy of offering to do as much training and other military activity inside Pakistan as the Pakistani government is willing to accept.
"It's their country," Gates said. "They remain in the driver's seat, and they have their foot on the accelerator."