South Korea' will act' against provocation from North
1 April 2013 Last updated at 16:12 BST
South Korea's president has promised a strong and swift military response to any provocation from the North.
It comes after North Korea announced it was in a ''state of war'' with its southern neighbour.
Pyongyang has also threatened to close a joint industrial complex which is a crucial source of foreign currency.
Lucy Williamson reports from the crossing into the joint industrial zone.