North Korea threatened retaliation against South Korea over what it claimed were naval drills around their disputed sea border, accusing Seoul on Thursday of attempting to escalate tension.
The North's Korean Central News Agency cited an unidentified source as saying that the South Korean military staged underwater explosive exercises around the border _ the scene of a naval clash last month that left one North Korean sailor dead and three others wounded.
The drills represent "a threat and an unpardonable act of crime against us," KCNA said.
"We cannot but view this as a premeditated provocation aimed at raising tension in the militarily sensitive waters," it said. "We will deal a merciless retaliatory blow if the South Korean warlike forces keep staging military provocations" near the border.
A South Korean Defense Ministry official could not immediately confirm whether the military conducted such drills but said he was checking.
North Korea has often made such accusations and the South has rejected them. Pyongyang, known for its use of fiery rhetoric, also regularly threatens South Korea with destruction.
The communist North does not recognize the sea boundary, drawn by the United Nations at the end of the 1950-53 Korean War, and has long claimed that it should be redrawn farther south. The dispute led to deadly skirmishes in 1999, 2002 and last month.
Relations between the two Koreas soured badly after conservative South Korean President Lee Myung-bak took office early last year and halted unconditional aid to the North in line with his pledge to get tough on the communist neighbor over its nuclear weapons development.
The two sides are still technically at war as the Korean War ended in a truce, not a peace treaty.