The North's navy command said in a statement the South's violations occurred several times on February 24, 27 and 28.

"We warn the South Korean military authorities that their act of perpetrating military provocations... would be a foolish act of digging their own graves," it said.

South Korea did not immediately respond to the statement. Seoul has rejected similar accusations as part of the North's military propaganda aimed at highlighting a disputed sea border in the Yellow Sea.

The two Koreas have remained technically at war since their 1950-1953 conflict ended in a fragile armistice, rather than a peace treaty.

North Korea has never recognized the sea border with the South that was drawn up by a US-led UN Command after the war, and it is a frequent flashpoint between them. Pyongyang puts the border further south.

The area was the scene of bloody naval clashes in 1999 and 2002 that resulted in heavy casualties on both sides.

The last clash in June 2002 left six South Korean sailors dead.

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