Anti-Taliban troops said they were making progress fighting their way into the mountains of eastern Afghanistan with tanks and mortars Thursday, as they attempted to push their way past foreign Al Qaeda fighters toward a cave complex where it is believed Usama bin Laden is holed up.

Mohammad Amin, a spokesman for Hazrat Ali, leading local fighters in pursuit of bin Laden, told Reuters by satellite telephone from Jalalabad that their forces had captured some cave-riddled hills of the Tora Bora complex, killing 22 foreign fighters.

Meanwhile, U.S. Marines outside the southern city of Kandahar moved into an offensive mode, tightening the siege around the Taliban's last stronghold by cutting off roads and communications to the city.

In the east, up to 1,500 tribal fighters pushed down a valley in the White Mountains toward the Tora Bora camp as American B-52s pounded the area with 250- and 500-pound bombs, setting off orange flashes and plumes of smoke in the forested mountains.

Anti-Taliban commanders said their troops advanced to within a mile of the anthill-like cave complex, sending the Arab, Chechen and Pakistani fighters loyal to bin Laden's Al Qaeda terror network scurrying to higher ground.

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

Afghan commander Amil Shah said Al Qaeda fighters in the area had nowhere to run, with escape routes into Pakistan to the east snowed in. "We are trying our best to capture them alive. They are surrounded by us, but they are not surrendering," he said.

Anti-Taliban forces advanced up the narrow, forested valley while their tanks shelled the hilltops a mile away. Al Qaeda fighters fired back with mortars and rocket-propelled grenades.

Local officials in Nangarhar province say they believe bin Laden is in Tora Bora — the name means "black dust" — although the Northern Alliance thinks he is in the Kandahar area more than 300 miles to the southwest.

Marines Shifting Gears Near Kandahar

In the south, Pashtun tribesmen pushed toward Kandahar, and U.S. Marines moved to increase pressure on the city.

"Opposition groups are now closing in on Kandahar," Maj. James Parrington, executive officer of the Marine Expeditionary Unit 15th's Battalion Landing Team 1, said, referring to the Afghan forces. "We are supporting them by conducting offensive operations."

The Marines will cut off roads, pathways and other routes that could be used by the Taliban either to bring in reinforcements or escape, Parrington, 37, of Minneapolis, told journalists at the base, called Marine Forward Operating Base Rhino.

Reconnaissance units were identifying key pieces of terrain north of Kandahar. They "are getting themselves in position to cut lines of communication," he said. Both the Marines and their Pashtun allies were getting into "position to defeat Taliban forces outside of Kandahar," he said.

Marines from Base Rhino were called into action on Wednesday after an errant U.S. bomb killed three U.S. servicemen and five anti-Taliban Afghan fighters and wounded 20 Americans and around 18 Afghans.

Parrington said other troops at the base were aware of the incident and that it has steeled them for the fight.

"This is real. We're not playing around. There are people out there who mean us ill will. It is serious," Parrington said. He added that the Marines were excited at the prospect of taking the fight to the Taliban and their Al Qaeda allies.

U.S. officials in Washington have said the Marines were not expected to take part in street fighting to drive the Taliban from Kandahar.

But the Marines' new move to help constrict the siege of the city was a major change for their mission so far.

The Associated Press contributed to this report.