KIRKUK, Iraq — A suicide bomber detonated an explosives-rigged vehicle at a checkpoint in northern Iraq on Sunday, killing seven police, and gunmen shot dead three people, officials said.The suicide bombing at the police checkpoint northwest of the city of Kirkuk also wounded 11 police officers. Anti-government militants frequently target the security forces, some of whom are poorly trained and lacking in discipline.The latest violence comes amid a protracted surge in nationwide bloodshed that has claimed more than 2,550 lives so far this year and sparked fears of Iraq slipping back into the all-out sectarian killing of 2006 and 2007.Iraq's first general election on April 30The unrest has been driven principally by widespread anger among the Sunni Arab minority over claims of mistreatment at the hands of the Shiite-led government and security forces, as well as by the civil war in neighbouring Syria.Iraq's first general election since American troops left at the end of 2011 will be held on April 30, in a major test for the security forces. While they were able to keep violence to a minimum during last year's provincial polls, the security forces have failed to halt a subsequent year-long surge in unrest.