As the international community grapples with how best to stymie North Korea's nuclear development, South Korea is making one move on its own. It's shutting down the last remaining vestige of inter-Korean cooperation, the Kaesong Industrial Complex.

The special zone, located north of the border just six miles inside of North Korea, employs an estimated 55,000 North Koreans. South Korea's government and industries pay to operate the park. A total of 124 South Korean companies run businesses and factories there, mostly making goods like shoes and clothing.

The reason for the shutdown is simple: "Assistance and the efforts of our government have ultimately been wrongly harnessed in the service of upgrading North Korea's nuclear weapons and long-range missiles," South Korea's Unification Ministry said in a statement.

South Korea estimates that since it opened in 2004, more than half a billion dollars has flowed into North Korea through business at the complex — $120 million in 2015 alone. It's a source of hard currency for a heavily-sanctioned North Korea, where it can be tough to get hands on hard currency.

"It appears that such funds have not been used to pave the way to peace as the international community had hoped," the Unification Ministry said.

The Kaesong complex has been subject to partial closures and temporary work stoppages during times of inter-Korean tensions. In 2013, Pyongyang effectively shut down the park by withdrawing its workers for five months. This year, following the Jan. 6 nuclear test by North Korea, South Korea put a cap on the number of its workers who could go there.

South Korea says Kaesong will be shut down indefinitely.

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