SEOUL, South Korea (AP) — North Korea says it will abandon its joint factory park with South Korea and turn it into a military zone if Seoul applies sanctions at the site, which is the rivals’ last remaining symbol of detente.

The threat Wednesday night comes amid tensions over the North’s announcement last month that it plans a third nuclear test.

Seoul said earlier this week it would step up inspections of cargo shipped into the Kaesong factory park, just north of the Koreas’ border. Seoul says that’s in line with U.N. sanctions over Pyongyang’s long-range rocket launch in December. The U.N. considers the launch a banned missile test.

Pyongyang says tougher inspections would damage relations.

Kaesong combines inexpensive North Korean labor with South Korean capital and knowhow, generating much-needed cash for the impoverished North.