Afghan warlords are intensifying their assault on the Tora Bora caves near Jalalabad amid claims Osama bin Laden's son is trapped there.
But there is still no sign of his father, who may have fled the White Mountains during the fighting around the fortress.
Tribal fighters say they are now within 500 yards of al-Qaeda position. In the valley below, tribal fighters are reinforcing their positions with more heavy weaponry.
"We don't have any confirmed information about Osama bin Laden, but his son is still in the caves," said Mr Haji Musa, the brother-in-law of provincial military chief Mr Hazrat Ali.
Heavy bombs from the high-flying US B-52s are targeting the higher slopes of the mountains which are the terrorists' only escape route.
Aging Soviet-built tanks have been firing repeatedly into positions held by al-Qaeda fighters, most of them Arabs and other foreign bin Laden loyalists.
Opposition forces have captured an area below the mountainside complex. At least four Arabs were killed and eight others wounded, according to witnesses.
Opposition commanders say tribal warriors had captured two caves yesterday - which they described as the command centre of the underground network - but retreated after finding them abandoned.
AP