At least four mortars have hit a compound housing the US-led administration in Baghdad.

There were no casualties.

Earlier, four Iraqis were killed, two of them policemen, by a bomb blast in southern Iraq.

The explosion in the port of Basra also wounded nine people, including school children.

A British military spokesman said the bomb blew up prematurely at 8.30am killing the man planting it and wounding his three accomplices, while two civilians passing in a car were also wounded.

Violence also shook the capital as a bomb attack on a Baghdad courthouse left two Iraqi police and four prisoners wounded.

Meanwhile, in the town of Haditha 120 miles west of the capital, witnesses said hundreds of demonstrators ransacked the police station and city hall.

In a separate development, the top US commander in Iraq, Lieutenant General Ricardo Sanchez, said 20 suspected al-Qaeda fighters had been captured.

The coalition acknowledged that its soldiers shot and killed a local Baghdad official in Sadr City, a volatile Shi'ite neighbourhood where clashes have already claimed the lives of US troops.