North Korea has threatened to shell South Korea if activists in the South send anti-Pyongyang leaflets over the border.
The North's official Korean Central News Agency said Friday that the Western Front Command of the Korean People's Army would conduct a "merciless strike" without warning on northwestern Phaju City, where activists say they will launch balloons Monday carrying the leaflets.
The KCNA accused South Korea's military of directly engineering propaganda, but Seoul has said it has nothing to do with the launches.
North Korea has lashed out at previous balloon launches, threatening to shell South Korea in response to such actions, which it calls deliberate provocation by Seoul that could lead to war.