Hundreds of South Koreans were expelled from a joint industrial zone in the North as part of the restrictions. Tourism trips and a cargo train to North Korea were suspended last week.

The RoK has funded the Kaesong industrial complex just over the border in the North, and a ban on border crossings would make it very difficult for the plant to continue operating.

Some 30,000 North Korean workers are employed by RoK companies at the complex.

Relations between the Koreas have become increasingly strained since February when President Lee Myung-bak took office in Seoul, pledging to get tough with Pyongyang over its nuclear weapons programme.

Last week South Korean activists sent thousands of propaganda leaflets into the DPRK, ignoring threats from the country to sever relations.