virus outbreak -- has not confirmed a single case of the disease that has swept the world since first emerging in China, the North's key ally.Pyongyang closed its border with China in January to try to prevent contamination, and in July state media said it had raised its state of emergency to the maximum level.US Forces Korea (USFK) commander Robert Abrams said that the border shutdown had increased demand for smuggled goods, prompting authorities to intervene.The North introduced a new "buffer zone, one or two kilometers up on the Chinese border," Abrams told an online conference organized by the Center for Strategic and International Studies (CSIS) in Washington on Thursday."They've got North Korean SOF (Special Operations Forces) out.