SEOUL, South Korea — South Korea warned of undefined reprisals unless North Korea agrees to talks aimed at re-opening a jointly run industrial park that has been shuttered for more than two weeks.

President Park Geun Hye’s government “will be forced to take serious measures” if the North refuses negotiations on the Gaeseong industrial zone, Unification Ministry spokesman Kim Hyung Suk told reporters Thursday in Seoul.

He called on North Korea to respond by Friday morning, while declining to elaborate on what steps might be taken.

The Korean peninsula has been on edge since February, when Kim Jong Un’s regime detonated a nuclear device in defiance of United Nations sanctions then threatened preemptive nuclear strikes against its enemies.

The North on April 8 recalled its workers from Gaeseong, the last point of inter-Korean exchange and a source of hard currency for its impoverished nation.

The complex, about 10 kilometers (6 miles) north of the demilitarized zone between the two countries, employs more than 53,000 North Koreans for 123 South Korean companies.

North Korea generates $100 million in annual profits there, while South Korea makes quadruple that amount, according to Yang Moo Jin, a professor at the University of North Korean Studies in Seoul.

With the United States and South Korea calling on North Korea to return to negotiations, Park’s options in pressuring Kim over Gaeseong “are very limited,” said Kim Young Yoon, a research fellow at the Korea Institute for National Unification in Seoul.

Jeopardizing Efforts

“Removing South Korean workers, assets and companies from Gaeseong or taking some military action against the North for not responding to calls for dialogue, will jeopardize all diplomatic efforts and what little that’s left to salvage deteriorated ties,” Kim said.

Currently 177 South Koreans remain in Gaeseong, the Unification Ministry spokesman Kim said.

Kim Jong Un, who took over as leader in December 2011 following the death of father Kim Jong Il, has rebuffed international inducements to abandon nuclear weapons development in favor of maintaining his family’s military-first policy.

The Obama administration has rejected claims North Korea possesses the ability to launch nuclear-armed ballistic missile while warning Kim’s inexperience raises the possibility of errors.

The risk of a miscalculation in the dispute over North Korea’s nuclear and missile programs has increased, the chairman of the U.S. Joint Chiefs of Staff said Wednesday in Beijing.

China, North Korea’s biggest ally, regards the situation “very seriously,” General Martin Dempsey told reporters after meeting officials including President Xi Jinping.

‘Still Time’

“We think there is still time for North Korea’s leaders to back away from provocations and we hope they take the opportunity to do so,” Dempsey said.

China regards its neighbor as a strategic buffer with U.S.- backed South Korea. Secretary of State John Kerry said ahead of meetings this month in Beijing that Xi’s government needs to “put some teeth” into restraining Kim’s regime. In a sign of greater cooperation, China said its North Korea envoy, Wu Dawei, will visit Washington this week for talks.

Deputy Secretary of State William Burns is also visiting Beijing this week.

The North is ready to conduct another nuclear test “at any moment,” South Korean Defense Ministry spokesman Kim Min Seok said on April 23. North Korea vowed to strengthen its nuclear program after a State Department report found the country guilty of “egregious and pervasive” human rights abuses.