Kim Jong-un, top leader of the Democratic People's Republic of Korea (DPRK ), has signed an order of battle to counter possible attacks by the Repulic of Korea (ROK) and the United States, the official news agency KCNA said Sunday.

Seoul and Washington are staging large-scale war drills targeting the DPRK, Kim said Saturday during a speech marking the 52nd anniversary of the start of the "military-first revolutionary leadership" of his late father Kim Jong-il.

"If the enemies fire even a single shell on our inviolable territory and territorial waters, the Korean People's Army (KPA) should deal prompt deadly blows at them and make an all-out counter-offensive to achieve national reunification," Kim was quoted as saying.

The KCNA said Kim examined the operation plan and signed it. He also asked the KPA to stay on high alert against "reckless moves" by the enemies.

Kim, also supreme commander of the KPA, vowed on August 18 to "turn the west sea into a graveyard of the invaders" during a visit to a front-line artillery unit near the tense western sea border.

The South Korea-US joint war games, code-named Ulchi Freedom Guardian, started on Monday and would last for 12 days. Some 56,000 South Korean troops and 30,000 US soldiers are involved. The two countries said the exercises were "defensive in nature".