Mahmoudiya, Iraq ? With a thunderous rumble and cloud of dust and smoke, an apparent suicide vehicle bomb brought down a section of highway bridge south of Baghdad on Sunday, wounding several U.S. soldiers guarding the crossing and blocking traffic on Iraq’s main north-south artery.

U.S. troops and private security guards, in black, work to remove concrete rubble from atop wounded soldiers at a bridge destroyed by an apparent suicide vehicle bomber Sunday outside Mahmoudiya, about 20 miles south of Baghdad.

There was no immediate U.S. Army confirmation on the number and severity of the casualties. An Iraqi civilian also was injured, said Donald Campbell, of the private security Armor Group International, who helped in the rescue.

Campbell, a 40-year-old from Inverness, Scotland, was among those in a passing Armor Group convoy who worked with a U.S. Army quick reaction force for some 45 minutes to pull trapped men from the rubble, scrambling over the fallen concrete.

U.S. armored vehicles provided cover fire from their cannons after the bombing, which occurred in the area dubbed the “triangle of death” for its frequent Sunni insurgent attacks.

The blast dropped one of two sections of the “Checkpoint 20” bridge crossing over the north-south expressway, six miles east of Mahmoudiya.

It appeared that a northbound suicide driver stopped and detonated his vehicle beside a support pillar, said Lt. Col. Garry Bush, an Army munitions officer who was in the convoy, which also carried an Associated Press reporter and photographer and arrived two minutes after the blast.

A U.S. Army checkpoint and a tent structure, apparently a rest area, fell into the shattered concrete. The crossing was believed to have been closed to all but military traffic at the time.

Armor Group security guards, all ex-military, and others in the convoy rushed to the ruins. They found a scene of confusion.

“When that size blast went off, everyone was in shock,” said one of the first atop the rubble, Jackie Smith, 53, of Olathe, Kan., a former lieutenant colonel now working as a civilian Army munitions expert.

He said he saw what he believed was the engine block of a truck – apparently what remained of the suicide vehicle.

Soon the outpost sergeant in charge was organizing a search for his missing men, Smith said. The Armor Group team climbed up with first-aid kits, stretchers and other aid.

During the rescue, U.S. armored vehicles opened up with suppressing fire, possibly having spotted movement in the surrounding countryside, flat and baking in 100-degree-plus temperatures.