South Korea is moving forward with a live fire military exercise 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 "legitimate" drills conducted in South Korea's own territorial waters. He said it will proceed as planned.
Early Tuesday, Kim said a North Korean fax message warned of unspecified "grave consequences" unless the South stops the drills held on the Yeonpyeong and Baengnyeong islands.
"We stressed to North Korea that our military is maintaining a firm readiness for a possible provocation by the North and will strike back if provoked."
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.
The exercises 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.
Kim Min-seok says the exercises and the reunions should not be treated as related issues.
"From the humanitarian perspective, reunions of separated families should take place. At the same time, we should conduct a military exercise to maintain a proper military capability, therefore the two issues should be delinked."
Inter-Korean relations had shown signs of improvement in recent weeks, with both sides at least speaking of the need to improve ties.
But many expect heightened tensions between the two Koreas next month, when the United States and South Korea begin large-scale, annual joint military drills.
The United States and South Korea have shrugged off North Korea's demands the drills be halted. The North views them as preparation to invade. Seoul and Washington say they are defensive in nature.
The two Koreas remain in a technical state of war, since the 1953 agreement that ended hostilities between them was only a truce.
(This report was produced in collaboration with the VOA Korean service.)