North Korea remained silent on South Korea’s proposal for final talks to reopen a suspended joint industrial park for a fifth day on Friday, sparking speculation that Seoul might be forced to take “grave” measures, South Korean News Agency (Yonhap) reported. The factory zone in the North Korean border city of Kaesong has remained shuttered since early April when Pyongyang withdrew all its workers amid heightened inter-Korean tensions. The Koreas have held six rounds of talks aimed at normalizing the complex, but to no avail. Seoul delivered the last overture on Monday.