WASHINGTON: The United States questioned Monday how Osama bin Laden had managed to hide out undetected in a Pakistani compound, after the Al-Qaeda leader was killed in an overnight raid by US special forces.

Counter-terrorism chief John Brennan said it was “inconceivable” bin Laden had not had some kind of support system as he managed to live “for an extended period of time” in a heavily-fortified compound barely two hours drive from Islamabad.

Laying bare Washington's mistrust of its “war on terror” ally, he revealed that the Pakistani government had only been notified of the raid after the elite team of Navy SEALs had left Pakistan's airspace.

“We are looking right now at how he was able to hold out there for so long and whether or not there was any type of support system within Pakistan that allowed him to stay there,” Brennan told a White House briefing.

A top US lawmaker also said Pakistan must prove to the United States that it did not know Bin Laden was hiding in a compound in Abbottabad.

“This is going to be a time of real pressure” on Pakistan “to basically prove to us that they didn’t know that bin Laden was there,” Senate Homeland Security Committee Chairman Joseph Lieberman said at a news conference.

Bin Laden, after apparently trying to use one of his wives as a human shield, was shot dead in a night-time helicopter raid by US commandos, ending a decade-long manhunt for the mastermind of the 9/11 attacks.

A day after announcing the success of the military operation in a dramatic televised address, President Barack Obama spoke for a second time on the killing, saying the “world is safer, it is a better place.”

DNA tests confirmed the body was that of bin Laden, a senior US official said after the assault on the Al-Qaeda leader's compound in the garrison town of Abbottabad, north of Islamabad.