Four people were killed by a roadside bomb in Baghdad's Sadr City on Monday morning, Iraqi police and medical officials said. An Iraqi police official said the bomb targeted a minibus in the busy al-Hamza Square in the Shiite slum of Sadr City. The official and a medical official say four civilians were killed and 11 others injured. Both officials spoke on condition of anonymity because they were not authorized to release information to the news media. Monday's attack was the second in two days in Sadr City, where Iraqi Prime Minister Nouri al-Maliki sent troops last year to wrestle control from a militia led by radical Shiite cleric Muqtada al-Sadr.