US Secretary of State Hillary Clinton has assured South Korea of America's full backing in the growing crisis over the sinking of one of its warships.With tensions rising rapidly, the North has reacted angrily to trade and shipping sanctions announced by the South.
It said on Wednesday it would cut off a road link across the heavily defended border if Seoul resumed propaganda broadcasts, halted six years ago.
Earlier, the North said it would match Southern sanctions with its own, and sever the few remaining lines of communication between the two governments.
South Korean ships and planes would be banned from Northern territorial waters and airspace.
All South Korean workers in the jointly run Kaesong industrial park north of the border were expected to be expelled although they were allowed to enter on Wednesday, Reuters news agency reports.
Apart from Kaesong, there is little economic relationship left between the two states, their ties almost frozen since Lee Myung-bak took office in 2008, the agency notes.
"North Korea is not closing up Kaesong immediately because it is saving the cards it needs in order to play the game," said Jang Cheol-hyeon, a researcher at the Institute for National Security Strategy.
The two states are technically still at war after the Korean conflict ended without an armistice in 1953.
South Korean K1 tanks could be seen on Tuesday conducting an exercise to prepare for a possible surprise attack by North Korea.
