North Korea gets 24-hour ultimatum from South Korea on formal talks about their joint Kaesong industrial zone Four more South Korean workers return from the Kaesong industrial zone as Northern officials bar business owners trying to deliver food to 205 remaining staff. South Korean workers talk outside the inter-Korean transit office after being refused access to Kaesong joint industrial park in North Korea, in Paju on April 3, 2013. North Korea blocked South Korean access to a key joint industrial zone on April 3, in a sharp escalation of tensions as Washington condemned Pyongyang's "dangerous, reckless" behaviour. SOUTH Korea has offered North Korea formal talks on suspended operations at their joint Kaesong industrial zone and hinted it might pull out entirely if Pyongyang declines. The South says it has proposed working-level talks to resolve the impasse over Kaesong, a rare symbol of inter-Korean co-operation that has become the most notable victim of escalating military tensions on the Korean peninsula. But the offer came with an ultimatum of unspecified "significant measures" if Pyongyang fails to accept the proposal within 24 hours. "There is no change on our stance to support the stable operation and improvement" of Kaesong, Unification Ministry Spokesman Kim Hyung-Seok said on Thursday. (FILES) This file photo taken on May 26, 2005 shows North Korean workers at a factory of a South Korean apparel maker in the inter-Korean industrial park in Kaesong, just a few hundred metres (yards) north of the heavily fortified Demilitarised Zone (DMZ) that divides the Korean peninsula. North Korean workers failed to report to work on April 9, 2013 at the joint Kaesong industrial zone with South Korea after Pyongyang suspended operations, upping the pressure on Seoul in an escalating military crisis. North Korea announced it was taking the unprecedented step of temporarily shutting Kaesong down on April 8, following a tour of the zone by senior ruling party official Kim Yang-Gon. The project was born out of the "Sunshine Policy" of inter-Korean conciliation initiated in the late 1990s by South Korean President Kim Dae-Jung which led to a historic summit with North Korean leader Kim Jong-Il in 2000. It operates as a collaborative economic development zone that hosts South Korean companies attracted by cheap, educated, skilled labour. Turnover was reported at $A459.42 million in 2012, with accumulated turnover since 2004 standing at $A1.94 billion. The Korean peninsula was already engulfed in a cycle of escalating tensions - triggered by the North's nuclear test in February - when Pyongyang decided on April 3 to block all South Korean access to Kaesong. Angered by the South Korean defence minister's remarks on a "military" contingency plan to protect South Korean staff in Kaesong, the North pulled out its entire workforce on April 9 and suspended operations. Since then it has denied repeated requests to send food and other supplies to South Koreans who opted to remain in the zone to maintain their non-running production lines. The association that represents the South Korean firms in Kaesong said it hoped the working-level talks would begin "as soon as possible." In a statement, it noted the agreement establishing Kaesong committed both sides to keep the zone going for 50 years. "Businessmen in Kaesong will not give up the right guaranteed by both governments," the statement said.