The first official talks between North and South Korean officials have ended without progress.
The North says the South Korean military moved a marker on the heavily armed border dozens of metres to the north, calling the move a "serious military provocation'' and a "vicious criminal act".
The North's official Korean Central News Agency (KCNA) said the country warned it would "take a measure for self-defence and the South Korean warmongers will be held entirely accountable for all the ensuing consequences" unless the
marker is returned to its original place.
North Korean officials also announced during the brief talks that they would not release a detained South Korean worker. He was arrested last month for allegedly denouncing the country's political system.