South Korea is moving forward with a live fire military exercise Tuesday near its tense border with North Korea, which has warned of "grave consequences" in response.
Seoul Defense Ministry spokesman Kim Min-seok defended the artillery exercise as a "legitimate" drill, conducted in South Korea's own territorial waters. He said it will proceed as planned.
Earlier Tuesday, Kim said a North Korean fax message warned of unspecified "grave consequences" unless the South stops the drills, which are to be held on the Yeonpyeong and Baengnyeong islands.
The North regularly makes such threats in response to South Korean exercises in the region. Though hostilities rarely break out, North Korea did shell Yeonpyeong in 2010, killing four South Koreans.
Inter-Korean relations had shown signs of improvement in recent weeks, with both sides at least speaking of the need to improve ties.
However, many expect tensions between the two Koreas to heighten next month, when the United States and South Korea begin large-scale, annual joint military drills.
The U.S. and South Korea have shrugged off North Korea's demands the drills be halted. The North views them as preparation to invade, while Seoul and Washington say they are defensive in nature.
The drills come as the two sides negotiate the resumption of reunions of families separated since the end of the Korean war six decades ago.
Last week, Pyongyang proposed restarting the family reunions, which were stopped in 2010 following the Yeonpyeong shelling. Seoul welcomed the offer, but is waiting on North Korea's response.
The two Koreas remain in a technical state of war, since the 1953 agreement that ended hostilities between them was only a truce.