A fresh US air strike has left at least four people dead and six others wounded in Baghdad's Sadr City district, Iraqi officials say.

The air strike just after midnight was near Al-Albaith mosque in the centre of Sadr City, the stronghold of cleric Moqtada al-Sadr. Police say that two of the dead were brothers aged seven and nine.

The Mahdi Army and Iraqi forces along with US troops have been involved in fierce clashes since March 25 after Prime Minister Nouri al-Maliki ordered a security crackdown in the southern city of Basra.

Some of the Iraqi cities have seen numerous US air and ground strikes since March 25. Scores of civilians including women and children were killed during the strikes.