The attempt marks the first time the group has been able to launch an attack on US soil. And while US officials have downplayed the threat — citing the bomb's lack of sophistication — the incident in Times Square and the Christmas Day airline bomb attempt indicate growing strength by overseas terrorist groups linked to Al-Qaeda even as the CIA says their operations are seriously degraded.

The finding also raises new questions about the US relationship with Pakistan, which is widely known to have Al-Qaeda and other terrorist groups operating within its borders.

On Sunday, suspected US missiles killed 10 people in a militant-controlled region of Pakistan close to the Afghan border, the first such strike since an alleged Pakistani-trained extremist Faisal Shahzad was accused of the Times Square attack.

Attorney General Eric Holder said that new evidence shows that the Pakistani Taleban was “intimately involved” in the bombing plot. John Brennan, the president's homeland security and counterterrorism adviser, made similar remarks, linking the suspected bomber to the Tehrik-e-Taleban Pakistan, or TTP.

“We know that they helped facilitate it,” said Holder. “We know that they probably helped finance it. And that he was working at their direction.” A US citizen of Pakistani descent, Shahzad is accused of spending 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-Qaeda and the Pakistani Taleban operate. He was arrested aboard an Emirates Airlines jet in New York just minutes before it was scheduled to take off for Dubai.

The link between an attack on US soil and terrorist groups operating inside Pakistan opens up a new chapter in relations between the two countries. Brennan said Islamabad was being very cooperative in the investigation but that the US 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.”