Pyongyang on Wednesday blocked South Koreans from entering a joint factory complex just north of the heavily fortified border, prompting Seoul to warn that it would take military action should its workers’ safety be compromised.

The North’s Central Special Direct General Bureau informed Seoul early in the morning that it would only allow the departure of South Korean officials and employees from the Gaeseong Industrial Complex.

The Unification Ministry urged immediate renunciation of the decision and vowed to ensure the safety of the people remaining there through its emergency round-the-clock contact network and some 1,300 civilian communication channels. 

“We deeply regret that the entry to the Gaeseong Industrial Complex was not processed normally this morning,” spokesman Kim Hyung-suk told a media briefing.

“This step poses hurdles for stable operation of the complex. We urge North Korea to normalize access to the complex immediately.”

In the border city of Paju, 484 officials and workers who gathered to go to work turned back home.

Only 33 employees came home throughout the day, compared with the initially planned 446. The difference largely results from 391 people who intended to enter and leave the district within the day, while the remainder opted to delay their departure on concerns over any manufacturing delays and the ensuing revenue shortfall.

After their return, 815 South Koreans will stay at the complex, the ministry said.

Associations for South Korean businesses at the industrial park gathered or issued a statement, urging North Korea to let in foodstuffs and industrial supplies, and the Seoul government to defrost the cross-border ties.

“I have no worries for now because there is a supermarket inside. But if the period extends, there will be a problem sourcing manpower and raw materials,” a 44-year-old female employee of a clothing firm told reporters upon arrival at the Gyeongui Highway Transit Office in Paju at around 2 p.m.

With the citizens’ safety being the top priority, Defense Minister Kim Kwan-jin said he was crafting various plans to deal with any contingency including military action.

“We must avoid the Gaeseong Industrial Complex situation coming to the worst,” he was quoted by Saenuri lawmaker Won Yoo-chul as saying at a special security panel meeting held by the ruling party.

“We are adamant to warn North Korea to refrain,” Kim said, adding that his agency has set up “all kinds of measures against any incident including military action.”

The notice is the latest in a recent string of Pyongyang’s protests against recent U.N. sanctions and annual military exercises by Seoul and Washington, including threats to annul the 1953 truce and stage atomic and missile strikes on the allies.

The totalitarian country last week severed its cross-border military hotline used to facilitate South Koreans’ entry to and exit from the joint factory zone. The two sides have since then been mobilizing another outlet held by the Gaeseong Industrial Complex Management Committee.

On Tuesday, the regime pledged to reactivate a graphite-lod nuclear reactor to extract plutonium for its weapons program in line with its new two-pronged policy of building atomic arms and boosting the economy.

As tension continued to escalate, China’s Foreign Ministry later that day separately called in South and North Korean ambassadors in Beijing to deliver its concern and urge calm.

After his talks with Seoul’s Foreign Minister Yun Byung-se in Washington, U.S. Secretary of State John Kerry warned North Korean leader Kim Jong-un to cease “provocative, dangerous and reckless“ acts, and vowed not to accept the unruly country as a nuclear state.

“I reiterate again the United States will do what is necessary to defend ourselves and defend our allies, Korea and Japan. We are fully prepared and capable of doing so, and I think the (North) understands that,” he told a joint news conference.

The two top diplomats agreed to “further strengthen credible and robust deterrence vis-a-vis North Korea’s nuclear and conventional provocations,” Yun said.

By Shin Hyon-hee (heeshin@heraldcorp.com)