North Korea doesn't want a war but its people are ready to "dedicate their blood to defend their inviolable territory," officer Sin Chol Ung at the North's Korean People's Security Forces said on Sunday.
South Korea plans to stage regular one-day artillery drills on Monday from front-line islands off the western coast.
Pyongyang says the drills are a reckless military provocation and the North will launch what it calls "merciless" strikes if the training is implemented.
The North frequently issues similar rhetoric against South Korea, but the latest warning comes 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. A 2010 drill triggered a North Korean artillery bombardment that killed four South Koreans.
The Korean peninsula remains technically at war because the 1950-53 Korean War ended with an armistice, not a peace treaty.
The Associated Press contributed to this report.