American B-52s dropped 250- and 500- pound bombs onto an elaborate tunnel and cave complex at Tora Bora overnight and Thursday morning.

Dozens of planes flew bombing missions over the rugged White Mountains near the northeastern city of Jalalabad, setting off orange flashes and plumes of smoke.

The airstrikes were preceded by anti-Taliban forces using tanks and mortars to attack Al Qaeda fighters loyal to prime Sept. 11 terrorist suspect Usama bin Laden, who local tribesman believe is holed up in the Tora Bora caves.

The tribesmen suspect bin Laden is being protected in the fortified cave complex by Arab, Pakistani and Chechen supporters. As many as 1,500 tribal fighters pushed down a valley toward the suspected hideout.

Residents in Jalalabad, 35 miles to the northeast, said shock waves from the early morning airstrikes were rattling the windows of their houses.

Doctors at Jalalabad's main hospital said that an officer, from the eastern Shura anti-Taliban group, and five of his men were wounded in an Al Qaeda ambush.

At the Pentagon, spokesman Rear Adm. John Stufflebeem said U.S. special forces were in the area helping direct airstrikes and were gathering intelligence. He said Afghan fighters had already entered some caves in the hunt for Al Qaeda members.

Commanders in the biggest anti-Taliban faction, the Northern Alliance, however, say it is more likely that bin Laden is hiding somewhere around the southern city of Kandahar.

Meanwhile, Taliban leader Mullah Mohammed Omar agreed Thursday to hand over control of the militia's last bastion at Kandahar to an opposition commander, Fox News has confirmed.

U.S. Marines who have been building up a base in the desert outside Kandahar for days have now moved to offensive operations for the first time, helping to cut off roads and communications into the city and cutting off possible Taliban escape routes, U.S. officials said.

Maj. James Parrington, an operations officer at the base, said Marine reconnaissance units were already identifying key pieces of terrain to be used in sealing off the city.

"Opposition groups are now closing in on Kandahar," he said. "We are supporting them by conducting offensive operations."

President Bush launched military operations in Afghanistan on Oct. 7 after the Taliban rulers refused to hand over bin Laden.

The Associated Press contributed to this report.