The soldiers from the Third Infantry Division were killed in an "apparent RPG attack", said Major General Buford Blount.

The soldiers were in Humvee all-terrain vehicles in a support unit for an artillery battalion when a moonless night allowed Iraqi fighters to sneak up within several hundred yards (metres) of them, said Blount, commander of the Third Infantry Division.

"It was zero illumination," he said of the attack, which occurred around 3:00 am (1200 midnight GMT) near a bridge captured by US troops on Wednesday.

In the early hours of Thursday, the Iraqis launched a counter-attack to try to recapture the key bridge south of Baghdad but were repulsed, US officials said.

Some 500 Iraqis were killed in fighting for the bridge over the Euphrates River, 30 kilometres (20 miles) from Baghdad, Major John Altman, an intelligence officer with the 1st brigade of the Third Infantry Division said earlier.

The Pentagon said late Wednesday the Iraq war had left 49 US troops dead, 40 of them in combat, seven known prisoners of war, 15 missing and 150 wounded. A US F/A 18 Hornet fighter and Blackhawk helicopter have since gone down.

The latest attack resulted in the first combat deaths for the Third Infantry Division.

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