There are further signs of mounting tension between the two Koreas.
Officials expelled from a joint industrial park in the North have returned to the South. In tit for tat action, North Korea has also announced that South Korean ships and airliners have also now been banned from passing through North Korean territory.
International investigators last week ruled that a torpedo fired from a North Korean submarine sank a South Korean warship in March, killing 46 sailors.
The US today described the incident as an unacceptable provocation, and said the international community has a duty to respond.
North Korea says it’s cutting all ties with the South, in response to the claims about the sinking. Pyongyang is also threatening to close the last road link between the two countries.
As demonstrations against the North are held in Seoul, the government says its measures against the North include the reestablishment of speakers near the border to broadcast anti-government propaganda.