SEOUL, South Korea— North Korea says it is firing artillery off its west coast as part of an annual military drill and will continue to do so.

The General Staff of the (North) Korean People's Army said in a statement that artillery units staged an annual live shell firing drill off the west coast Wednesday morning.

The statement — carried by the official Korean Central News Agency — said such drills "will go on in the same waters in the future, too."

South Korean officials said the North fired about 30 rounds of artillery from its coast and the South immediately responded by firing 100 warning shots from a marine base on an island near the disputed sea border.

The western sea border is a constant source of tension between the Koreas. (AP)