Hundreds of local people marched in the town of Falluja after the attack, chanting slogans praising ousted Iraqi leader Saddam Hussein and denouncing President Bush.

U.S. soldiers sealed off and searched part of the town, about 60 miles from Baghdad, after the attack. A military medical helicopter took casualties from the scene.

"An IED (improvised explosive device) exploded beneath a bridge," the spokeswoman said. The attack happened around 1:30 p.m. (5:30 a.m. EDT) but few other details were available, she said.

Local people said a U.S. military vehicle had been damaged by the bomb.

U.S. forces occupying Iraq following the war that ousted Saddam have come under frequent attack in Falluja. It forms part of a mainly Sunni Muslim region north and west of Baghdad which was the bedrock of support for the former president.