A series of bombs went off simultaneously killing at least four people and wounding nine others in a mainly Sunni residential area in the Iraqi capital on Friday, security sources said.

An Interior Ministry source said five bombs were planted around four houses in the same neighbourhood in Baghdad's western Ghazaliya district.

Two bombs were stuck on doors, two were planted in gardens and one was a roadside bomb on the street in front of the houses, the source said.

A police source said the blast killed four people and wounded 11 others. Another police source said five people were killed.

Violence has dropped sharply in Iraq since the peak of sectarian fighting in 2006-07 but bombings and other attacks still occur daily as the army and police battle Sunni insurgents and Shiite Muslim militias.