Lieutenant Colonel Pete Owen said reinforcements had been sent overnight to the front line, where a marine battalion was taking on Iraqi fighters using rifles, automatic weapons and rocket-propelled grenades.

Three marines had already been wounded Tuesday evening in a battle that erupted after US troops swarmed into Baghdad across the Diyala river.

Military sources later said that the marines were continuing to encounter stiff resistance.

"We are worried about collateral damage with regard to civilians," one officer told AFP.

"The Iraqis have managed to slow us down but they have not stopped us in our tracks. We are approaching this in the same manner we have approached every other battle since the war started."

Commander Ken Kelly, from a Shock Trauma Platoon, said most of the six injured marines had been hit by shrapnel while the more seriously wounded were shot by rifle fire.

"Much of the shrapnel was to the arms and it is becoming evident that flak jackets and helmets are reducing the number of deaths and serious casualties," he said.

He added that the fighting had occurred in a sector of Baghdad allocated to the marines' First Regimental Combat Team and warned that further combat was expected.

"There is a need to secure the area and to work towards that key objective.

"Then the next phase of the war can begin and that will involve improving relations with the Iraqi people and carrying out more humanitarian work."

SPACE.WIRE