Marines placed a green metal shipping container in the middle of a detention facility they are building in their desert base and spoke to someone inside. A Marine spokesman declined to identify who was inside but said John Walker, the captured American Taliban fighter, is the only detainee on the base.

The container is about 10 feet high, 20 feet wide and 10 feet deep, sits on the desert floor and is overlooked by a guard tower. It is in the middle of the detention facility the Marines have set up just outside the walls of Camp Rhino.

Marines stood next to it, one with his face close to the container's side, as they spoke to someone inside.

Asked if the 20-year-old Walker was inside the box, Marines spokesman Capt. Stewart Upton said this: "I have no information for you at this time." But minutes earlier, another spokesman, Capt. David Romley, confirmed that there was only one detainee in the camp — Walker.

Walker, of Fairfax, Calif., was found among Taliban fighters held at a fortress in northern Afghanistan after an uprising by the prisoners was put down in late November. U.S. officials have not decided how his case will be handled.

Off the air base, Marines worked Tuesday to cut off escape routes for fighters from Usama bin Laden's Al Qaeda network and their Taliban allies, intercepting vehicles to search for top enemy officials and weapons.

The mission was particularly sensitive, since the American forces were trying to avoid agitating civilians, who often carry guns for self-protection. It also was likely that former fighters may have slipped into everyday clothes.

"You can't let your guard down," Maj. Chris Hughes said at the Marine air base in southern Afghanistan. "You can't tell the enemy just because he has a different uniform on. It is an asymmetrical war."

The Marines, carrying photos of Al Qaeda and Taliban leaders, had the discretion to let cars with weapons pass if they felt the arms were for family protection.

"We don't want to upset the Afghani people that have helped us in trying to win this war," Upton said back at Camp Rhino. "The war on terrorism is still going on."

Confiscated weapons were photographed and recorded by their serial numbers before being destroyed.

Romley could not say how many weapons — if any — had been seized so far in the weapons-checking process that began this week.

More than 1,300 Marines are on the ground in Afghanistan, working with British, German and Australian forces.

The air base has been in operation for two weeks and over 800 sorties have been flown in and out of it.

In their spare time, the Marines of Bravo Company were having a Christmas decoration contest, trying to find creative ways to make trees and ornaments. One method was filling the miniature Tabasco bottles that come in their MREs — Meals Ready to Eat — with colored water.

The Marines also continue to try and improve their spartan life, building makeshift gymnasiums and barbeque-type stoves, mostly to sit around at night for warmth and to heat water for coffee, tea and clothes-washing.