US officials have not explained how they managed to secretly fly four helicopters across the Pakistan border to near the capital and into a military garrison city that was home to the country's military academy. What's more, it remained unclear how the SEAL team was able to conduct what was described as a 40-minute mission, including a firefight and the explosives destruction of a helicopter, without the Pakistan military or police intervening.

Bin Laden's death came 15 years after he declared war on the United States. Al-Qaida was also blamed for the 1998 bombings of two US embassies in Africa that killed 224 people and the 2000 attack on the USS Cole that killed 17 American sailors in Yemen, as well as countless other plots, some successful and some foiled.

The greatest terrorist threat to the US is now considered to be the al-Qaida franchise in Yemen, far from al-Qaida's core in Pakistan. The Yemen branch almost took down a US-bound airliner on Christmas 2009 and nearly detonated explosives aboard two US cargo planes last fall. Those operations were carried out without any direct involvement from bin Laden.

Retaliatory attacks against the US and Western targets could come from members of al-Qaida's core branch in the tribal areas of Pakistan, al-Qaida franchises in other countries or radicalized individuals in the US with al-Qaida sympathies, according to a Homeland Security Department intelligence alert issued Sunday and obtained by The Associated Press.

A prominent al-Qaida commentator vowed revenge for bin Laden's death. "Woe to his enemies. By God, we will avenge the killing of the Sheik of Islam," he wrote under his online name Assad al-Jihad2. "Those who wish that jihad has ended or weakened, I tell them: Let us wait a little bit."

As quickly as bin Laden's supporters vowed to avenge his death, administration officials worked to undermine his reputation.

"Here is bin Laden, who has been calling for these (terror) attacks, living in this million-dollar-plus compound, living in an area that is far removed from the front, hiding behind women who were put in front of him as a shield. I think it really just speaks to just how false his narrative has been over the years," said Brennan.

Any hint of possible Pakistani collusion with bin Laden could hit only worsen US-Pakistani relations, which were already at a low point. Critics had long accused elements of Pakistan's security establishment of protecting bin Laden, though Islamabad has always denied this.

Relations between Pakistan's main intelligence agency and the CIA had been very strained in recent months after a CIA contractor shot and killed two Pakistanis in January, bringing Pakistani grievances out into the open. Since then, a Pakistani official has said that joint operations had been stopped, and that the agency was demanding the Americans cut down on drone strikes in the border area.

For now, the US and NATO are insisting that bin Laden's death will not trigger a rapid withdrawal from Afghanistan, where about 150,000 NATO troops are embroiled in daily fighting with Taliban insurgents. Obama committed 40,000 additional US troops to fight the Taliban fighters, but planned to start pulling out troops in July - if conditions allow.