South Korea says it has fired warning shots toward six North Korean fishing boats that crossed the disputed Yellow Sea border between the two countries.

Seoul's defense ministry, which confirmed the incident to VOA, says two South Korean navy patrol ships fired multiple rounds near the North Korean boats. Officials say none of the shots hit the fishing boats, which quickly returned to their side of the de facto western sea border.

It is not uncommon for North Korean fishing boats to violate the poorly marked border, which is not recognized by Pyongyang. Last week, Seoul reported that seven boats briefly crossed the demarcation line before being warned away by South Korean patrol boats.

But the Yonhap news agency says it is the first time the South Korean military has fired warning shots against North Korean vessels since November 2010, shortly after Seoul accused Pyongyang of a deadly attack on of one of its warships.

The two Koreas have been technically in a state of war for more than 60 years. The agreement that ended the 1950-53 civil war was only a truce.

North Korea wants the sea border, which was drawn up by the U.S.-led United Nations force following the conflict, to be drawn further south.