US Marines said they had launched an offensive in the Iraqi hotbed town of Fallujah where four US contractors were killed last week and two of them savagely mutilated. "Our concern is precise. We want to get the guys we are after. We don't want to go in there with guns blazing," said Lieutenant James Vanzant. The restive town, 50 kilometres (30 miles) west of Baghdad, has been sealed off and troops were only letting people enter or leave with Fallujah licence plates. An AFP correspondent said US forces had barricaded residents inside. Marine officers said the operation would last...