Thirty-one North Koreans crossed the tense sea border and arrived on a frontline South Korean island at the weekend, but it is unlikely they are defectors, the Seoul government said Monday.

The North Koreans, consisting of 11 men and 20 women, arrived on South Korea’s Yeonpyeong Island on a 5-ton fishing boat on Saturday. Their ship has been towed to a nearby port city for investigation, the South Korean military said.

Located just a few kilometers from North Korean shores, Yeongpyeong Island was the target of a deadly artillery attack by Pyongyang in November.

“The North Koreans are currently being questioned on how and why they crossed the border,” said Col. Lee Bung-woo, spokesman for South Korea’s Joint Chiefs of Staff.

None of the North Koreas have so far expressed willingness to defect, Lee said, adding weight to the possibility that the boat accidentally drifted into South Korean waters.

All 31 people will be returned to North Korea unless they express a desire to stay, according to South Korean law and past cases.

An unnamed government official had said earlier that the North Koreans appeared to have accidentally reached South Korean waters based on the fact that they were a working group and not family members. Heavy fog was hanging near the western sea border when the boat drifted toward the island, the official said.

The boat was spotted through the thick fog at around 11 a.m. Saturday by Seoul’s military stationed on Yeonpyeong Island.

The North Koreans’ arrival comes as the two Koreas prepare to hold working-level military talks on Tuesday ― their first official dialogue since North Korea’s bombing of Yeonpyeong in November last year.

Three officials from each side are due to meet 10 a.m. Tuesday at the inter-Korean border village Panmunjeom to discuss the agenda for higher-level military talks slated for later this month, Seoul’s Defense Ministry said.

Cross-border tensions have run high since Pyongyang conducted two deadly attacks against Seoul last year, killing dozens of young sailors as well as two civilians.

A sensitive issue for the impoverished North which relies mostly on outside aid to feed its people, more than 20,000 North Koreans have defected to the South since the 1950-53 Korean War, mostly via China.

The South Korean government said it will continue questioning the North Koreans on the possibility of defection.

There have been cases of mass defection by North Koreans via sea in the past. Twenty-one North Koreans arrived in South Korea on a fishing boat in 2002, while another 11 crossed the sea border on a barge in 2009.

By Shin Hae-in (hayney@heraldcorp.com)