KCNA said the North was also expelling all South Korean workers from a jointly-run factory north of the border.
The move comes after an international report blamed North Korea for sinking a South Korean warship.
Pyongyang denies it torpedoed the Cheonan near the inter-Korean maritime border on 26 March, killing 46 sailors.
How does this involve the United States? What is Secretary of State Clinton doing about this?
Revisit the new island shelling of South Korea by North Korea. What good can come of this? What is their goal?