A U.S. Army infantry battalion seized six vehicles loaded with weapons and ammunition, killed two men and captured 11 at an Iraqi air base outside An Nasiriyah, military police said.

U.S. forces sealed off 36 bunkers around the vast Tallil air base that had been earmarked as potential sites for possible weapons of mass destruction. Some of the bunkers, which were to be opened later with news media present, had been looted.

The three trucks, one fuel truck, one taxi and one bus were seized Monday when one of them tried to speed into the air base, which is under the control of U.S. forces, said Capt. Jeff Searl of the 709th Military Police Battalion.

All of the captured and killed were wearing civilian clothes, and it was not clear why the vehicle was headed toward the base. The men appeared to be trying to get hold of weapons from different caches stored earlier.

"There seems to be plenty of weapons around -- enough to cause concerns for the security of our troops," said Lt. Col. Richard Vanderlinden of Gladstone, Mich., commander of the MP battalion.

The unit is holding almost 250 prisoners of war, and MPs started putting up tents to protect them from sandstorms.

Two wounded POWs have died in the past two days, despite receiving medical care. They were buried and their personal details were recorded so their families will be able to claim the bodies.

A large prisoner camp for 8,000 people is being built closer to the Kuwaiti border.