BAGHDAD — A local government official said gunmen attacked Iraq's largest oil refinery on Saturday, killing one guard and detonating bombs that sparked a fire and forced the facility to shut down.The spokesman for Salahuddin province, Mohammed al-Asi, said the assailants broke into the Beiji refinery, attacked the guards and planted bombs. One guard was killed and another wounded.Firefighters were trying to put out a blaze started by the bomb explosions.The refinery processes about 150,000 barrels of oil per day.Beiji is about 155 miles (250 kilometers) north of Baghdad.