Islamic militants laid siege to Iraq’s largest oil refinery Wednesday, threatening a facility key to the country’s domestic supplies as part of their ongoing lightning offensive, a top security official said. The attack comes militants have seized wide swaths of territory in Iraq – and as the specter of the sectarian warfare that nearly tore the country apart and the doubts that followed the 2003 U.S.-led invasion now haunt those trying decide how to respond. The official said fighters of the al-Qaida-inspired Islamic State of Iraq and the Levant began their attack on the Beiji refinery, some 250 kilometers (155 miles) north of the capital, Baghdad, late Tuesday night. The attack continued into Wednesday morning, with fighters targeting it with mortar shells. A small fire started on the facility’s periphery, he said. The official spoke on condition of anonymity because he was not authorized to speak […]