A North Korean patrol boat retreated after briefly crossing the western sea border into South Korea, Yonhap News Agency reported Thursday, citing South Korean military officials. \"A North Korean patrol boat crossed the Northern Limit Line and sailed up to 0.36 kilometers into waters east of South Korea\'s Baengnyeong Island at about 11 a.m. (0200 GMT) while trying to crack down on Chinese fishing boats illegally operating there,\" an official was quoted as saying. The North Korean vessel retreated at around 11:07 a.m. after warning signs were broadcast by the South Korean military. South Korea\'s Navy on Sept. 21 fired warning shots against North Korean boats operating south of the western sea border. 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. Pyongyang does not recognize the line, arguing it was unilaterally drawn by the US-led United Nations forces at the conclusion of the 1950-53 Korean War that ended in a truce. It has demanded that a new border be drawn further south.