The South and North Korean flags are seen from Paju, Gyeonggi Province, Friday. The government said it has tightened its military readiness posture to step up monitoring of North Korean military moves in the wake of the North's killing of a South Korean citizen. Yonhap

South Korea tightened its military readiness posture to step up monitoring of North Korean military moves particularly near the tense sea border in the wake of the communist country's brutal killing of a South Korean citizen, the defense ministry said Friday.

On Tuesday, North Korean troops shot the fisheries official who was adrift in its waters and incinerated his body. He went missing the previous day while on duty near the Yellow Sea border island of Yeonpyeong.

"Our military issued the instruction on Thursday that calls for the strengthening of the readiness posture regarding the current situation," the ministry's deputy spokesperson Col. Moon Hong-sik told reporters.

"The focus is on closely monitoring North Korean military moves around the clock and to maintain a firm defense posture to swiftly react to all circumstances so as to prevent the escalation of tensions."