South Korea on Tuesday carried out a live-fire drill on its northwestern islands despite North Korea's warning of "grave consequences," but the exercise ended without clashes with the North, Yonhap News Agency reported. Ahead of Tuesday's exercise, the North's National Defense Commission sent a fax through the western military hotline to urge South Korean President Park Geun-hye to cancel it, according to the report. "North Korea called on South Korea to stop the live-fire artillery exercise, threatening grave consequences," Defense Ministry spokesman Kim Min-seok was quoted as saying at a press briefing in Seoul. The South Korean defense ministry's policy director immediately replied to the North to stress that the naval drill is a "legitimate exercise" that is held in its own territorial waters, Kim said. The South Korean military is maintaining a firm readiness against any North Korean attacks and will strike back if provoked, Kim added. Later in the day, artillery batteries stationed at two islands located just south of the western maritime border carried out the live-fire exercise for an hour. There were no special movements by the North Korean military, the report said. Seoul has bolstered its capabilities near the border after the North fired artillery at Yeonpyeong island in 2010, which lies just 11 km from North Korean shores, killing four South Koreans. The two Koreas still remain technically at war after the 1950-53 Korean War ended in a truce.