Unification Ministry spokesman Kim Hyung-suk said Seoul wants an answer by Friday, Yonhap reported.
"We are making an official offer to North Korea to discuss ways of normalizing operations at the Kaesong Industrial Complex and want to hear their position on the matter before noon Friday," Kim said. "If Pyongyang does not respond by the deadline, Seoul will have no choice but to take serious measures."
Kim did not say what the measures would be.
He said North Korea turned down a request Wednesday for informal talks between South Korean representatives at the Kaesong Industrial District Management Committee in Kaesong, just north of the demilitarized zone, and North Korea's General Bureau for the Special Zone Development Guidance, which manages the industrial complex.
"They not only rejected the talks proposal but did not even bother to accept the list of humanitarian requests being made," the official said.
Kim said the informal discussions concerned allowing food and medical personnel in Kaesong to assist 176 South Koreans in the border town.
Observers said if North Korea refuses, South Korea will have to recall the South Koreans, Yonhap said. If that happens, North Korea could confiscate assets of South Korean companies.
Operations at Kaesong halted April 9 when Pyongyang withdrew its 53,000 laborers working for 123 South Korean companies. Six days earlier, the North barred South Korean personnel and industrial materials from entering the complex.
The crisis at the complex, which began operating in 2004, came as North Korea ratcheted up its rhetoric in recent months after it was sanctioned for its third nuclear test in February and a long-range rocket launch late last year.
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