South Korea warns North not to reject offer of talks on crisis at industrial zone

Seoul, South Korea (CNN) -- South Korea on Thursday warned North Korea of serious consequences if it rejects an offer to hold 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 over the zone, the Kaesong Industrial Complex, by noon on Friday.

Kim said that if Pyongyang turns down the offer, Seoul would have no choice but to take "grave" measures. He did not specify what those measures might involve.

A South Korean soldier stands on a road linked to North Korea at a military checkpoint in Paju on Wednesday, April 3. After a week of threats to the United States and South Korea, North Korea blocked hundreds of South Korean workers from entering the industrial complex, which is an important symbol of cooperation between the two countries.

South Korean soldiers walk down the empty road after trucks were denied access to the Kaesong joint industrial park in North Korea.

South Korean trucks turn back after they were banned from entering Kaesong.

An officer directs a South Korean car that was denied access at a military checkpoint in Paju.

A South Korean military vehicle leads cars arriving from the Kaesong joint industrial park to Paju.

South Koreans stand in front of an information desk at the Inter-Korean Transit Office in Paju after being blocked from North Korea.

South Korean trucks turn back.

A truck drives back toward Paju.

Reporters gather in front of customs at the Inter-Korean Transit Office in Paju.

A South Korean soldier walks past a Kaesong Industrial District Management Committee bus at the Inter-Korean Transit Office.

Koreans blocked from the North

Koreans blocked from the North

South Koreans blocked from the North

South Koreans blocked from the North

South Koreans blocked from the North

South Koreans blocked from the North

South Koreans blocked from the North

South Koreans blocked from the North

South Koreans blocked from the North

South Koreans blocked from the North

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Photos: Koreans blocked from the North

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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.

Since the North started preventing people from entering the zone from the South Korean side, the number of non-North Koreans in there 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.

CNN's K.J. Kwon reported from Seoul, and Jethro Mullen reported and wrote from Hong Kong.