A coordinated string of four bomb attacks within seven minutes killed at least 18 people and wounded 39 in northern Iraq Tuesday, while a Baghdad car bomb injured 28, officials said, ending a relative lull in violence that had fallen over the country in recent days.Hundreds of U.S. and Iraqi soldiers descended on the remote northern city of Tal Afar near the Syrian border on Tuesday, launching a major operation against insurgents following weeks of attacks against Iraqi security services there, military officials said. Two U.S. Marines died Monday after separate roadside bombings near Fallujah, 40 miles west of Baghdad, the military said Tuesday. Tuesday’s attacks in northern Iraq appeared coordinated and aimed at checkpoints manned by members of Iraq’s fledgling army, which has been a constant target of insurgents opposed to the country’s new U.S.-backed government.Full Story