Violence focused mainly on security checkpoints killed 13 people in Iraq Thursday, as the country struggles with daily unrest ahead of next week's parliamentary election. Iraq is suffering a protracted surge in bloodshed that has killed more than 2,800 people this year, and Wednesday's polls -- the first since US troops departed in 2011 -- will be a major test for security forces. A car bomb exploded at a police checkpoint near the city of Hilla, south of Baghdad, killing eight people, among them three police, and wounding 20, an officer and a doctor said. And four soldiers were shot dead in an attack on a checkpoint south of the northern city of Mosul, while a man was killed in a shooting in the city. Security forces were able to keep violence to a minimum during provincial elections last year, but they have failed to halt a subsequent year-long surge in unrest. The heightened violence has been principally driven by widespread anger among the Sunni Arab minority, who say they are mistreated by the Shiite-led government and security forces. It has also been fuelled by the bloody civil war in neighbouring Syria, which has bolstered militant groups. Violence in Iraq has killed more than 560 people since the beginning of the month, according to AFP figures based on security and medical sources.