Hunt for bin Laden heats up

US bombers are attacking al-Qaida's Tora Bora cave complex as the hunt for Osama bin Laden is stepped up.

Air strikes hit Tora Bora where some say bin Laden is sheltering.

There were reports the US had dropped its powerful "daisy-cutter" bombs.

Thousands of Pakistani troops have been deployed along the border near Tora Bora in an attempt to prevent fleeing al-Qaida forces entering the country.

Helicopters dropped personnel on mountain ridges to monitor the movement of the Islamic militants.

Afghan tribal fighters drove Soviet-built tanks closer toward enemy positions at Tora Bora.

But they were forced back when al-Qaida troops resurfaced from the caves and fired mortars ahead of the armoured convoy.

There was a brief exchange of fire, but no casualties were reported.

Constant bombing by B-52s and other US warplanes has aimed to weaken al-Qaida defences ahead of an anticipated ground assault by as many as 2,500 Afghan tribesmen.

It is unclear when the attack will be launched. Haji Zahir, a militia commander and the son of provincial governor Abdul Qadir, said tribal forces would launch smaller guerrilla raids in the meantime.