South Korea ? The two Koreas briefly exchanged naval fire today along their disputed western sea border, with a North Korean ship suffering heavy damage before retreating, South Korean military officials said.

There were no South Korean casualties, the country’s Joint Chiefs of Staff said in a statement, and it was not immediately clear if there were any casualties on the North Korean side.

The North’s patrol boat crossed the disputed western sea border this morning, drawing warning shots from a South Korean navy vessel, the statement said. The North Korean boat then opened fire and the South’s ship returned fire before the North’s vessel sailed back toward its waters, the statement said.

The North Korean ship was seriously damaged while the South Korean ship was unscathed, a Joint Chiefs of Staff officer said. The officer spoke on condition of anonymity, citing department policy.