North Korea is to close all land borders with South Korea from 1 December, accusing its neighbour of taking confrontation beyond the danger level.
North Korea's KCNA news agency says it has officially informed the South that the North Korean army will cut off all overland passages through the Military Demarcation Line.
The move follows increasingly angry comments against South Korea's conservative government, which came to power earlier this year with a promise to get tough if North Korea did not give up its nuclear weapons programme.
The little traffic across their heavily armed border is the product of agreements during 10 years of left-leaning leaders in Seoul.
Relations between the states have increasingly frayed since February when conservative president Lee Myung-bak took office pledging to get tough with Pyongyang but offering economic aid if it mended its ways.
Last month, North Korea threatened to reduce the South to rubble unless it stopped civic groups from sending anti-Pyongyang leaflets into the communist state. Analysts say the recent flood of such leaflets had rattled the North's leaders.
"The leaflets are going deeper into the country than before and this has increased concern in North Korea, especially because it comes at a time when there is speculation on (leader) Kim Jong-il's health," a South Korean government source said.