``The alert is in response to a probability that some North Korean armed agents could have come ashore undetected,'' said Col Hwang Dong-Kyu, a spokesman for the Joint Chiefs of Staff. South Korean President Kim Dae-Jung ordered a thorough search for possible infiltrators from North Korea, with which South Korea technically remains in a state of war.

The alert was issued after the body, clad in a wet-suit, was found on a beach two km from a major South Korean naval base on the east coast.``From the various equipment and personal belongings found, it appears certain that the body is that of an armed North Korean agent,'' the Joint Chiefs of Staff said in a statement.

The statement said the body was found washed ashore near Donghae, 195 km east of Seoul, and the military immediately increased land and sea patrols in thearea. The military later put all units in the area on increased alert after a self-propelled, semi-submersible craft, capable of helping infiltrate up to five agents, was found near where the body was found.

The craft, made of aluminum, was similar to the ones used by North Korean agents to infiltrate into South Korea in the past, military officials said. ``The size of the cone-shaped craft indicates that some armed agents might have come ashore undetected,'' Hwang said.

Quoting military doctors, the Joint Chiefs of Staff said the body was believed to have been dead ``24 hours to 48 hours'' when it was found.The body was found along with a Czech-made machine gun, a hand grenade, a portable oxygen tank, a dagger and a radio set, it said. The military ruled out the possibility that the body was that of an agent from a North Korean submarine found off the east coast last month. In 1996, a Shark-class North Korean submarine was found stranded off South Korea's east coast, touching off a 53-day manhunt for thecraft's 26 occupants who came ashore. The manhunt by 60,000 soldiers, reservists and police left 37 people dead 24 North Koreans and 13 South Koreans.