ISHIGAKI, Japan — South Korean patrol boats fired warning shots at North Korean fishing vessels in contested waters in the Yellow Sea on Friday, but the North’s boats fled without casualties, the South Korean military said.

The episode took place in South Korean-controlled waters along the western coast of the Korean Peninsula, not far from Yeonpyeong Island, the scene of a deadly North Korean rocket barrage two years ago. Naval clashes have been common in this area because North Korea has never recognized a sea boundary set by the United Nations after the 1950-53 Korean War.

That demarcation line was drawn without the North’s consent, making it one of the most likely spots for confrontation between the two Koreas, which are still technically in a state of war. Two and a half years ago, a South Korean warship, the Cheonan, blew up in this area in a mysterious attack in which South Korea and its allies blamed a North Korean torpedo. The North has denied being behind the sinking, which killed 46 sailors.

On Friday, two South Korean patrol boats fired warning shots at six North Korean fishing vessels that had sailed about half a mile into South Korean-controlled waters, the South Korean military said in a statement. North Korean warships were not involved.