North Korean leader Kim Jong-un paid a visit to the front-line artillery unit responsible for the country's 2010 deadly bombardment of a South Korean island, extolling service members as heroes and telling them never to tolerate enemy aggression, state media said Saturday.

The visit to the unit on the North's border island of Mudo came days before South Korea and the United States are to launch their annual joint exercise, Ulchi Freedom Guardian. The computer-aides exercises, set for Aug. 20-31, will mobilize some 56,000 South Korean troops and about 30,000 U.S. soldiers.

The North's artillery unit shelled the South Korean border island of Yeonpyeong in November 2010, killing two civilians and two soldiers. It marked the North's first attack on South Korean soil since the end of the 1950-53 Korean War, though the sides have fought naval skirmishes.

The North claimed at the time that it acted in response to a joint military exercise between South Korea and the United States in waters near the western sea border. The region has been a source of military tensions, as Pyongyang does not recognize the boundary.

"The enemy troops on Yonphyong (Yeonpyeong) Island recklessly fired shells at the islet without knowing from where the deadly blows were dealt and they were hit hard by the telling shells fired by the service personnel of the detachment here with towering hatred," Kim said during the visit, according to an English-language dispatch released by the Korean Central News Agency.

The North's leader also proposed to award "the title of hero to artillery piece No. 1 and the title of heroic defense detachment to the Mu Islet Defense Detachment for demonstrating the mettle" of the country's armed forces, the KCNA said.

"This islet is not only biggest hotspot on the Korean Peninsula but a very sensitive area on which the world attention is focused and where the interests of many countries are intermingled," Kim said, denouncing military exercises by South Korean and U.S. forces in the area as "reckless" moves threatening peace and stability.

The young leader told service members to be "vigilant against every move of the enemy and not to miss their gold chance to deal at once deadly counter-blows at the enemy if even a single shell is dropped on the waters or in the area," the KCNA said. (Yonhap News)