A police officer says the parked explosives-laden vehicle went off today morning in Karrada neighbourhood, near a commercial area and some government offices.
Three civilians and two policemen were killed and at least 12 people were wounded in the explosion.
A medical official confirmed the causality figures. Both officials spoke on condition of anonymity because they were not authorised to talk to media.
Since last year, Iraq has been seeing the worst level of violence since the nation emerged from Shiite-Sunni bloodletting in 2008.