North Korean leader Kim Jong-un inspected Navy units in the western sea, Pyongyang said Saturday, as the communist country continued to ratchet up threats against South Korea.

Kim accompanied several military commanders on a tour of a defense unit on Cho Islet, some 70 kilometers west of the North's capital Pyongyang, and then visited Navy Unit 123, the Korean Central News Agency (KCNA) said.

"Saying that Cho Islet is a gate to the West Sea and Pyongyang is behind the islet, he instructed the service personnel of the defense unit to consolidate the combat positions as firm as a rock," the KCNA said in an English report.

Kim's military inspection came days after South Korean Defense Minister Kim Kwan-jin made a rare trip to Yeonpyeong Island to vow launch powerful retaliation against North Korea if provoked again amid a spate of militaristic rhetoric by Pyongyang.

The North shelled the frontline island of Yeonypyeong in November 2010, killing two South Korean marines and two civilians.

The young leader, believed in his late 20s, has toured the heavily armed border with the South and a visited a number of military units, apparently seen as efforts to seek to bolster support.

"He instructed the service personnel to step up combat preparations, always aware that their positions allow no retreat and there is no place to retreat even an inch there, and thus mercilessly wipe out the aggressors should they come in attack," the KCNA said.

The latest remark also came a day after South Korea and United States forces wrapped up their 12-day joint annual military exercise, called the Key Resolve.

North Korea made war threats before and during the exercise last month, accusing the South and the U.S. of preparing for a northward invasion, though no actual attack has occured.

Seoul and Washington say their exercises are routine and defensive in nature.

The two Koreas remain technically at war with each other since their 1950-53 conflict ended with a truce, not a peace treaty.