North Korea fired artillery into the sea Wednesday near its disputed border with South Korea and South Korean forces fired back, Seoul officials said.
The North's artillery batteries on land fired into waters near the border shortly after 9:00 am (0000 GMT), a spokesman for the Joint Chiefs of Staff said.
"Our military immediately fired back in response," a Seoul presidential official told AFP on condition of anonymity.
The incident came a day after the North declared a "no sail zone" around the tense border, which was the scene of deadly naval clashes in 1999 and 2002.
Another clash in November left a North Korean patrol boat in flames.