SEOUL, South Korea (AP) _ After abandoning their submarine on South Korea's east coast, 11 North Koreans apparently committed suicide today and a 12th was captured in an extensive manhunt near the rugged, mountainous shore.

Thousands of South Korean soldiers and police scoured a thickly wooded mountain that rises from the shore for eight more North Koreans believed to have come ashore, South Korean officials said. The active search was halted at nightfall, with soldiers ordered to lie in ambush until dawn.

The captured North Korean said the submarine carried 20 men when it ran aground on a reef off Kangnung, 90 miles northeast of Seoul, according to Brig. Gen. Shin Sang-gil.

Gen. Chung Hwa-un said it was unclear whether the submarine was trying to land spies in South Korea or had become stranded during a training exercise. The North Koreans found all wore civilian clothes and white sneakers.

There was no immediate North Korean reaction to the apparent infiltration, certain to strain already tense relations between the Koreas.

Shin said the 11 dead intruders were found on shore about five miles southwest of the stranded sub at 5 p.m., about 15 hours after the craft was spotted in the surf just yards off the coast.

Shin said 10 of the bodies were together, and the eleventh a short distance away. He speculated that the eleventh intruder killed his companions then shot himself in a mass suicide. A handgun was found on his body.

Associated Press Television reported that 10 bodies were lying in a row, each shot in the face.

Police captured the North Korean in a village about two miles inland. He was carrying a loaded pistol, but offered no resistance.

SBS-TV, a private South Korean network, said the captured intruder told police the submarine developed engine trouble shortly after leaving its home port of Wonsan on the North's east coast Monday. It drifted across the border, the intruder, identified as Li Gwang Sup, 31, reportedly said.

Gen. Chung said soldiers searching the submarine found a piece of paper that read: ``We accomplish (the) mission without fail.'' They also found a Czech-made machine gun, a North Korean-made automatic rifle, 175 rounds of ammunition, and 100 hand grenades.

The 60-foot submarine, made mostly of plastic to evade radar detection, weighs about 70 tons, the Defense Ministry said.

It was the first reported North Korean infiltration since October, when a Communist agent was shot to death and another captured in a gunfight near Puyo in central South Korea. Three South Korean policemen also were killed.

The area where the submarine was found today, 60 miles south of the border, is near the spot where 1,000 North Korean troops landed at the start of the 1950-53 Korean War.

It also is near where more than 100 armed North Korean guerrillas infiltrated in 1968. In a weeklong manhunt, five intruders were captured, two turned themselves in and the remainder were killed. Some 70 South Korean soldiers and civilians also were killed.

The two Koreas never signed a peace treaty after the Korean War ended, and their border remains the most heavily guarded in the world. Nearly 2 million troops are deployed on both sides.

``This is a clear violation of the armistice,'' said Lt. Gen. Kim Dong-sin, who directed the search.

At first, the ministry said the submarine could have carried up to 10 men, but later said it might have carried 20 or more.

Helicopters flew overhead earlier today, directing soldiers searching the area. Out at sea, about a dozen navy ships guarded against a possible North Korean attempt to assist the fleeing intruders.

Defense Ministry officials said air force jets were standing by. All roads leading to the mountains were cut off, and citizens were ordered to report all strangers. Area residents were placed under a dusk-to-dawn curfew.