According to a report on Tuesday, a South Korean naval ship fired warning shots at a North Korean patrol boat that crossed into contested waters west of the Korean Peninsula.
After the South Korean vessel opened fire, the patrol boat retreated.
The South Koreans then boarded a second ship carrying seven North Koreans, all of whom were dressed in military uniforms except one.
The incident occurred along the Northern Limit Line, a western sea barrier that has seen a number of skirmishes over the years.
The North Koreans said under questioning that they had no intention of defecting and that their ship had crossed the Northern Limit Line by accident, according to the South Korean military.
Following the armistice that ended hostilities in the Korean War in 1953, the boundary was created. Pyongyang has previously opposed to the line’s location, claiming that it is too far north.
The border was drawn when the two countries signed an armistice in 1953.
When North Korean boats wander south of the maritime boundary, Seoul’s policy is to return the occupants to Pyongyang’s territory unless they demonstrate a desire to defect.
The event took place on the eve of South Korea’s presidential election on Tuesday.