North Korea has called South Korea's president a "pro-U.S. fascist maniac" and a "chieftain of evils" because he placed his troops on high alert after leader Kim Jong Il's death.
The North's Committee for the Peaceful Reunification of Korea said Wednesday that the North Korean army would force South Korea to pay a price for the action.
North Korea has regularly blasted South Korean President Lee Myung-bak since he ended a no-strings-attached aid policy toward the impoverished North after taking office in 2008.
It also criticizes Lee's government for barring all South Koreans, except for two private delegations, from visiting to pay respects after Kim's death.
The statement was carried by the official Korean Central News Agency.