South Korea warned of an unspecified “grave measure” if North Korea rejects talks on a jointly run factory park shuttered for nearly a month, setting up the possible end of the last remaining major symbol of inter-Korean cooperation. In a televised briefing with reporters on Thursday, Unification Ministry spokesman Kim Hyung-suk refused to describe what Seoul would do if Pyongyang does not respond by a deadline Friday to a demand for formal working-level talks on the industrial complex just over the heavily armed border in the North Korean town of Kaesong. But Seoul’s talk of a “grave measure” may be an attempt to signal it will pull out its remaining workers from the complex. “There is no change on our stance to support the stable operation and improvement” of Kaesong, Kim said. “But we cannot let this situation continue as it is,” he added. “If North Korea rejects our proposal… we have no choice but to take significant measures.” Kim did not elaborate on what steps might be taken, but the ultimatum suggested South Korea was considering a permanent withdrawal from the zone, which normally employs 53,000 workers at 123 South Korean companies. The talks proposed by Seoul would be between the respective heads of the North and South committees that oversee Kaesong operations.