KABUL, Afghanistan — Two armored Humvees were missing from a U.S. military base in Afghanistan, a military spokesman said today.

The military was investigating whether the vehicles were stolen, although officials believed they were likely still in the possession of U.S. personnel but simply unaccounted for, said Lt. Col. Paul Fanning.

The two vehicles were reported missing on May 6 from U.S. Camp Phoenix in the capital, Kabul, Fanning said.

"We have a witness from our own teams here that says he saw them last being operated by U.S. personnel," Fanning said. "We are tying to locate where they are precisely."

The Humvees have electronic equipment designed to thwart homemade bombs.