US lawmakers demanded to know how the world's most wanted man could have resided -- apparently for years -- in a comfortable home in Abbottabad, a hillside retreat close to Islamabad popular with retired Pakistani generals.

Pakistan will need to "prove to us that they didn't know that bin Laden was there," said Senator Joe Lieberman, the chair of the Homeland Security Committee, predicting "real pressure" on Islamabad.

Senator Susan Collins, the top Republican on the same committee, called for "more strings attached" to the billions of dollars which the United States offers Pakistan in military assistance.

"I think that this tells us once again that, unfortunately, Pakistan at times is playing a double game and that is very troubling to me," she said.

But the Obama administration carefully avoided criticising Pakistan. Announcing bin Laden's death late yesterday, Obama said that "our counter-terrorism cooperation

with Pakistan helped lead us to bin Laden."

"Going forward, it is essential that Pakistan continue to join us in the fight against al Qaeda and its affiliates," Obama said.