The U.S. military said engineers were dispatched with bulldozers and other heavy equipment to clear the highway, which was partially blocked by debris from the overpass. An Iraqi interpreter also was wounded in the attack, according to the statement that gave the casualty toll.
Donald Campbell, a 40-year-old Scot with the private security firm Armor Group International, and his colleagues were in a passing convoy and 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, which crosses 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, 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.
With the Army's quick reaction force, they struggled to lift concrete shards off the men, pinned along the slope of what was once a roadway. At one point, 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 a black T-shirt-clad Briton administered painkiller to the freed man.
"Another poor fellow looked crushed beneath a concrete slab," said the Armor Group's Campbell.
During the rescue operation, U.S. armored vehicles opened up with suppressing fire, possibly having spotted movement in the surrounding countryside, flat and baking in 100-degree-plus Fahrenheit temperatures.
In other developments: