South Korea says it is closely monitoring the North Korean military's movements in cooperation with the United States.

Defense Ministry spokesperson Choi Hyun-soo said on Tuesday that the South Korean military is maintaining a readiness posture for all situations.

The spokesperson, however, didn't elaborate on a possible adjustment of posture in border areas and along the western coast, which has been the site of previous inter-Korean military skirmishes.

Choi also reaffirmed Seoul's position that the military tension-easing agreement signed between the two countries in 2018 must be fulfilled.

Earlier on Tuesday, the General Staff of the Korean People's Army(KPA) said it is reviewing a plan to reenter zones that had been demilitarized under the inter-Korean deal and "turn the front line into a fortress."