South Korea's Navy fired warning shots against North Korean boats operating south of the western sea border, military officials said, after raising the alert status in response to a number of ships violating the demarcation line over the past week.

The North Korean boats retreated to north of the border upon the warning shots, officials said.

The latest move comes as a growing number of North Korean boats have been seen fishing in waters south of the Northern Limit Line, the de facto maritime boundary between the two Koreas. (Yonhap News)