Seoul, South Korea (CNN) -- South Korea on Thursday warned North Korea of serious consequences if it rejects an offer for talks about the dire situation at their shared manufacturing zone where Pyongyang has halted activity amid recent tensions.
The South Korean Unification Ministry spokesman Kim Hyung-seok urged the North to respond to the offer of talks by noon Friday, saying South Koreans inside the zone, the Kaesong Industrial Complex, are facing "serious difficulties due to lack of food and medical supplies."
Kim said that if Pyongyang turns down the offer, Seoul would have no choice but to take "grave" measures regarding the zone. He did not specify what those measures would be.
Seen as the last major symbol of cooperation between the two countries, the Kaesong complex is a joint economic zone on the North's side of the border that houses the operations of more than 120 South Korean companies.
Earlier this month, during a frenzy of fiery rhetoric directed at South Korea and the United States, the North began blocking South Koreans from entering the complex across the heavily fortified border.
It then pulled out the more than 50,000 North Koreans who work in the zone's factories, saying it was temporarily suspending activity there. The move surprised some observers, since Kaesong was considered to be a key source of hard currency for the regime of Kim Jong Un.
The production halt was one of the most tangible signs of the heightened tensions on the Korean Peninsula in the past few weeks. The situation had deteriorated after the North carried out its latest underground nuclear test in February, prompting the U.N. Security Council to tighten sanctions on the regime in Pyongyang.
The tougher sanctions, together with joint U.S.-South Korean military training exercises in South Korea, generated an intensification in North Korea's threats against Washington and Seoul.
The North's fiery rhetoric, which unnerved the United States enough for it to move missile-defense systems into the region, has since appeared to calm somewhat. And the U.S.-South Korean military exercises are due to end in the coming days.
But the situation at the Kaesong complex remains up in the air.
Some South Koreans, who manage the factories in the zone, have remained inside since the North started preventing people from entering from across the border. If they leave, they don't know when they'll be allowed back in.
The number of non-North Koreans in the complex has steadily dwindled from more than 800 before the crisis began. As of Wednesday, 176 South Koreans and one Chinese person remained in the Kaesong complex, according to South Korean authorities.
Citing the difficulties experienced by those still inside the zone and the harm the situation is doing to the companies involved, Kim, the Unification Ministry spokesman, said Thursday that the complex couldn't be left as it is.
He said the talks South Korea is proposing would aim to "resolve the humanitarian problem" of those still inside the zone and to normalize operation of the factories.
"South Korea is signaling to the North that they are willing to consider the option of shutting down the Kaesong Industrial Complex," said Jasper Kim, founder of the Asia-Pacific Global Research Group in Seoul. "But in all likelihood that is not what it wants."
He said that although the economic cost of closing the complex would hurt the North more than the South, Seoul is more likely to be concerned about the political consequences of bringing an end to the symbol of cooperation.
There didn't appear to be an immediate reaction from North Korea on its state-run Korean Central News Agency.
CNN's K.J. Kwon reported from Seoul, and Jethro Mullen reported and wrote from Hong Kong.