SEOUL, South Korea  —  South Korea (search)'s navy fired warning shots Tuesday after a North Korean patrol boat entered waters controlled by the South, the military said.

The North Korean vessel turned back and there were no further hostile exchanges between the two sides, South Korea's Joint Chiefs of Staff said.

The patrol boat intruded three-tenths of a mile into southern waters along the disputed western sea border, South Korean officials said. A Southern navy speedboat fired two warning shots and the North Korean boat returned to communist territory three minutes later.

The maritime border between the two Koreas is not clearly marked, and North Korean fishing boats often cross over into South Korean waters. South Korean navy ships occasionally respond with warning shots.

The incident came just ahead of the scheduled six-way talks in Beijing this week.

Representatives from the United States, Japan, Russia, China and the two Koreas were scheduled to meet from Wednesday to Friday to discuss North Korea (search)'s nuclear ambitions.

The navies of the two Koreas, which were divided in 1945, fought deadly skirmishes in the western sea in 1999 and 2002.