The North's military said in a statement that South Korea planned naval shelling drills Monday in the waters around five front-line islands off the western coast, where it said the North maintains its sovereignty.
South Korean defense and military officials said they had no immediate knowledge of such drills. They said South Korea plans joint anti-submarine drills with the United States this week, but the training site is further south.
"Such move of the warlike forces is a premeditated military provocation ... to drive the overall situation on the Korean peninsula into the phase of war," a North Korean western military command said in a statement.
The North will launch "merciless retaliatory strikes" if the training is implemented, said the statement carried by the official Korean Central News Agency.
The North frequently issues similar rhetoric against South Korea without following through with its threats, but the latest warning come as ties between the Koreas remain tense following the death of North Korean leader Kim Jong Il in December.
South Korea has barred all of its citizens, except for two private delegations, from visiting to pay respects to Kim, and North Korea has vowed to retaliate.
South Korea regularly conducts artillery drills from front-line islands and a 2010 drill at one of the five islands, Yeonpyeong, triggered a North Korean artillery bombardment that killed four South Koreans.
"The Lee Myung-bak group of traitors should not forget the lesson taught by the Yeonpyeong Island shelling case," the North's statement said, referring to the South Korean president.
It warned all civilians living or working on the islands to evacuate before the drills start.
The two Koreas are still technically at war because their conflict in the early 1950s ended with an armistice, not a peace treaty.
