Yet another bridge in Iraq has come under attack.

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.

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 and others in a passing Armor Group convoy 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.

I believe the north-south highway is part of the main logistical routes supplying forces in Baghdad and north of there. It’s going to get harder and harder moving troops, food, water and other essential supplies.

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"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.

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 one of the black T-shirt-clad 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 over an hour until a medevac helicopter landed to take aboard the wounded, and traffic slowly resumed under the remaining section of the span.

Is it just a case of bad nerves when covering vehicles open fire with no apparent sign of attack? And why would it take an hour to get a medevac flight there? It looks to be less than 100 miles.

As COL Pat Lang noted last month, it’s beginning to look like an isolation strategy.

The campaign against the bridges continues in Baghdad. Two more bridges were attacked yesterday. These were across the Diyala River in southeast Baghdad. That makes five bridge attacks so far. Motive remains a question. My "working theory" is that the predominately Sunni insurgents are seeking to impede the "creeping" movement of Shia occupation of the city from east to west. A friend in Baghdad tells me that the "line" dividing the mainly Shia part of the city from the mainly Sunni is moving steadily westward to the disadvantage of the Sunnis. The goal would be a Shia dominated capital city. An alternative theory is that the insurgents are seeking to build impediments to the movement of coalition tactical reserves (QRF). Time will tell.

This attack was against a military target. The route was closed to civilian traffic.