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, trapping and wounding several U.S. soldiers guarding the crossing.

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.

However, The Washington Post reported that U.S. and Iraqi officials said at least three American soldiers who were nearby died in the blast, but reports conflicted on whether they were on the overpass or under it when the explosions occurred.

Campbell and others in a passing Armor Group convoy worked with a U.S. Army quick reaction force for about 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.

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.

Other troops struggled to lift concrete shards off the pinned men. A Bradley armored vehicle with a tow chain pulled a slab off a pinned victim to free him.

Then a shout went up, “Morphine! Morphine!” and one of the Britons administered painkiller to the freed man.

“Another poor fellow looked crushed beneath a concrete slab,” said Armor Groups Donald Campbell, 40, of Inverness, Scotland.

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.

Traffic was delayed for more than an hour until a medical helicopter landed to take aboard the wounded, and traffic slowly resumed under the remaining section of the span.

Separately, the U.S. military on Sunday reported the deaths of three American troops. Among them were a U.S. airman killed in a roadside bombing in southern Iraq; and two soldiers, one killed in Baghdad and another who died of injuries in Diyala province.

The deaths raised to at least 3,505 members of the U.S. military who have died since the Iraq war started in March 2003, according to an Associated Press count.

Elsewhere Sunday, a suicide truck bomber struck an Iraqi police office in Tikrit, killing at least 15 people and wounding 50, police said.