Continuing its sweep through Iraq, Islamic militants from ISIS have now laid siege to Iraq’s largest oil refinery. The Beiji refinery is located 155 miles north of Baghdad and produces roughly a quarter of Iraq’s oil output. The attack began Tuesday night and continued Wednesday morning with parts of the oil refinery in flames. Early Wednesday morning, the Iraqi Army claimed to have pushed back the militants at Beiji and killed 40 members of ISIS. "The situation in Tal Afar, Samarra, and Beiji is under control," the army said. If the refinery falls to militants, it would provide them with another big source of cash.