South Korean Army's K-9 self-propelled howitzers fire during a military drill against possible attack from North Korea near the demilitarized zone that separates the two Koreas since the Korean War, in Inje, South Korea, Thursday, Feb. 7, 2013. Without confirmation of when North Korea might carry out its vow to conduct its third nuclear test, the building suspense has prompted outsiders to look at dates Pyongyang has chosen for past atomic tests and rocket and missile launches.(AP Photo/Yonhap, Lee Jong-gun) Korea Out

Seoul, South Korea -

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 on Wednesday night comes amid tensions over the North's announcement in January 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 UN sanctions over Pyongyang's long-range rocket launch in December. The UN 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. - Sapa-AP