MAHMOUDIYA, Iraq — An apparent suicide car bomber took aim at an American convoy carrying demolition experts yesterday, collapsing a major highway overpass south of Baghdad and trapping American soldiers in the rubble.

The vehicle detonated beside a support pillar, bringing down an Army checkpoint and a tent that had been on the collapsing span, dubbed “Checkpoint 20” by the American military. The overpass, one of two crossing over Iraq’s main north-south highway in the region, appeared to be closed to all but military traffic at the time.

An American Army quick reaction force and the staff of Armor Group International, a private security firm that was in charge of the passing convoy, worked for some 45 minutes to pull trapped men from the rubble about six miles east of Mahmoudiya.

There appeared to be several casualties, including an Iraqi interpreter who was wounded, according to Donald Campbell, an official with the security firm who was at the scene.

The attack, which was witnessed by an Associated Press reporter and a photographer who were in the approaching convoy, occurred in the triangle of death, so called for frequent Sunni insurgent attacks.

On May 12, three American soldiers were captured in an ambush near Mahmoudiya that left five other soldiers, including an Iraqi, dead. A Qaeda front group the Islamic State of Iraq issued a video last week claiming the three missing troops had been killed, but the American military said it would not accept that and was continuing with its search. Iraqi police said the overpass was a vital link across the highway for villagers in the area because the other spans have been taken over by American forces.