SEOUL, South Korea - North Korea's military is threatening to attack a South Korean border area where anti-Pyongyang activists plan to launch leaflets from balloons.
North Korea has made similar threats without following through. Friday's vow comes a day after South Korea's president warned against provocation as he visited a front-line island shelled by North Korea in 2010.
South Korea's defence minister says his troops will retaliate if the North attacks.
South Korean activists regularly send up balloons carrying leaflets criticizing North Korean leaders.
The North says it will "strike mercilessly" if leaflets are flown as scheduled Monday. It also warns South Korean residents to evacuate.
The 2010 shelling killed four South Koreans. Seoul also blames Pyongyang for the deadly sinking of a warship that year. North Korea denies the claim.