SHATRA, Iraq (Reuters) - U.S. Marines have launched a dawn raid on the town of Shatra, north of Nassiriya, aiming to kill senior Iraqi officials they believe are directing guerrilla attacks, Reuters correspondent Sean Maguire has reported. Among those targeted was Ali Hassan al-Majeed, or "Chemical Ali", the cousin whom President Saddam Hussein has put in charge of the southern front. Majeed earned his nickname for overseeing the use of poison gas against Kurdish villagers in 1988. The Marines were storming the town, about 35 km (20 miles) north of the city of Nassiriya, with warplanes dropping precision-guided bombs, helicopter...