The Pentagon has confirmed a 15,000lbs "Daisy-cutter" bomb has been dropped at the Tora Bora cave complex, after a reported sighting of Osama bin Laden.
US forces deployed the weapon, it's most powerful conventional bomb, due to claims senior al-Qaida leaders - including bin Laden - had been seen at a cave entrance.
US Rear Admiral John Stufflebeem, of the Joint Chiefs of Staff, said the complex should now have been put out of use.
He said the target was being used by substantial al Qaida forces and senior leadership.
Asked if that included bin Laden, he said "yes" and added: "There are many reports that could have come from any quarters.
"Not all can be substantiated but in this case we decided to deny the cave entrance. In this case we used a bigger weapon to do that."
He said American special forces and local Afghan fighters had not yet been able to confirm if any al Qaida leaders were killed by the blast, which produced a cloud which obscured the mountains at Tora Bora for several minutes.
"It is still a hot area," said the admiral.
"So with the fighting that is going on, it is difficult to get into that area to assess the effect on the ground."