North and South Korea's navies have engaged in a short battle off their disputed western sea border.
North Korea is demanding an apology after a South Korean ship inflicted heavy damage on one of its vessels.
South Korean military officials say its vessel fired warning shots at a North Korean patrol boat after it crossed the disputed border.
When the North Korean boat opened fire, the South's ship returned fire before the North's vessel sailed back into its waters.
The North Korean ship was seriously damaged in the skirmish while the South Korean ship was unscathed, a Joint Chiefs of Staff officer said.
There has been no troop movements along the heavily-fortified border that separates the two Koreas.
The navies of the two Koreas fought their last skirmish in 2002 along the same western sea border area. Six South Korean sailors were killed during that confrontation.
The disputed border area is a rich crab fishing area.
The two countries have yet to agree on a sea border more than 50 years after the end of the Korean War.
The latest battle comes as the world's leaders share concern over the North's nuclear arms program.