Baghdad  - Joint US-Iraqi forces backed by helicopters attacked Saturday the Hayaniya district of Basra, where most of radical Shiite cleric Moqtada al-Sadr's close aides are concentrated, witnesses told Deutsche Presse-Agentur dpa.

Loud explosions were heard in southern Iraq's second largest city while intense clashes occurred between militants and US-Iraqi forces.

Witnesses said the attacks resulted in casualties, but reliable figures were not yet available.

Police and army troops have launched operations in the Hayaniya district in search of militants and criminal gangs with illegal weapons, Iraqi army sources told dpa.

On March 25, the Iraqi government launched a security operation in Basra codenamed "Charges of the Knights" aimed at militants and Moqtada al-Sadr's Mahdi Army fighters. (dpa)