SEOUL - The Republic of Korea and the United States on Monday launched a joint exercise aimed at enhancing defense readiness against potential security threats, military officials said.

The computer-assisted simulation exercise, dubbed Ulchi Freedom Guardian (UFG), will mobilize some 56,000 ROK's troops and 30,000 US forces.

"Ulchi Freedom Guardian is a key exercise in strengthening the readiness of Republic of Korea and US forces," Gen. James D. Thurman, commander of the US forces stationed in ROK, said in a statement.

"It is based on realistic scenarios and enables us to train on our essential tasks with a 'whole of government' approach," he added.

The Democratic People's Republic of Korea's army has been informed of the launch of the annual drill and its non-provocative nature, according to officials.

The DPRK, which is technically still at war with the ROK since the 1950-53 Korean War ended with a truce, warned last week the joint training can leFad to a "sacred war".

Kim Jong Un, top leader of the DPRK, inspected a front-line artillery unit days before Seoul and Washington are to launch their annual joint exercises, state media reported on Saturday.

During his visit to the unit of the Korean People's Army (KPA) on the DRPK's border Mu Islet on the southwest front, Kim praised service members as heroes and told them never to tolerate any enemy aggression, the official news agency KCNA reported.

"If the enemy dares recklessly preempt firing and even a single shell drops on the territory of the DPRK, the KPA should lead the battle to a sacred war for national reunification, not confining it to a local war on the southwest region," Kim was quoted by the KCNA as saying.

"He also ordered it to turn the west sea into a graveyard of the invaders," the KCNA report said.

Kim, also Supreme Commander of the KPA, carefully watched Yonphyong Island from the post and expressed satisfaction over the combat posture of the detachment, according to the report.

The DPRK and the ROK exchanged fierce artillery fire near Yonphyong Island in November 2010, killing four people of ROK. Both sides accused the other of firing the first shot.

"This islet is not only the biggest hotspot on the Korean Peninsula but a very sensitive area on which world attention is focused and where the interests of many countries are intermingled," Kim was quoted as saying.

Kim slammed the United States and the ROK for "threatening peace and stability of not only the DPRK but of the region and the rest of the world", as the two often stage provocative war drills in those waters of the sea.

The drill is scheduled to end on Aug 31.