Thirty-one North Korean people crossed the tense Yellow Sea border by boat and arrived on the frontline South Korean island of Yeonpyeong on Saturday in an apparent defection, a government source said Monday.
The North Koreans, consisting of 11 men and 20 women, arrived on Yeonpyeong Island by a fishing boat and were towed away to the western port city of Incheon, the source said on the condition of anonymity.
"Currently, a team of military and intelligence officials is interrogating the North Koreans on how they crossed the Yellow Sea border," the source said.
The source said the North Koreans are a "work group," not family members.
A military official, who also spoke on the condition of anonymity, said investigators are looking into the possibility that the North Koreans arrived on Yeonpyeong Island after drifting at sea.
There are no children among the North Koreans and they were believed to have left North Korea's western port city of Nampo, about 60 kilometers southwest of Pyongyang, according to the military official.
They were spotted in thick fog as of 11:00 a.m. on Saturday by the South's military stationed on Yeonpyeong, the official said.
"Given the circumstances so far, they might have been drifting after setting the wrong coordinates or losing power on their boat," the military official said.
It wasn't immediately known whether some of the North Koreans wished to defect to South Korea.
The arrival of North Koreans also comes at a sensitive time as military officials from Seoul and Pyongyang were set to hold their first dialogue on Tuesday since the North's deadly attack of Yeonpyeong last November.
Tensions on the Korean Peninsula have remained high since the North shelled Yeonpyeong, killing two civilians and two marines.
More than 20,000 North Koreans have arrived in South Korea since the end of the 1950-53 Korean War.