Prime Minister Lee Nak-yon said Friday that South Korea won't let its guard down and will ensure its defense against North Korea despite the recent conciliatory mood with the provocative communist nation.

Lee made the remark during a ceremony commemorating the North's 2010 sinking of the South Korean warship Cheonan near the western sea border, which left 46 sailors dead, and other battles with the North in and around the Yellow Sea.

Prime Minister Lee Nak-yon speaks during a ceremony held on Friday at a national cemetery in the central city of Daejeon to commemorate North Korea`s 2010 sinking of the South Korean warship Cheonan. (Yonhap)
"Touch-and-go military tensions that persisted until the end of last year are reversing into agreements on inter-Korean and US-North Korea summits. I hope the series of highest-level talks, which nobody had expected, will produce North Korea's denuclearization and permanent peace on the Korean Peninsula," Lee said.

"But we cannot loosen our natiaonal defense based only on this hope. We have to continue to invariably guard the West Sea and will do so. The government is well aware that we cannot ensure peace without firm national defense," he said during the ceremony at a national cemetery in the central city of Daejeon.

Lee said the waters near the Yellow Sea border face constant threats from the North.

"Our soldiers have risked their lives to guard the West Sea. We have not given up an inch of sea in the West Sea, and we cannot do so in the future," he said. (Yonhap)