South Korean authorities are investigating the crossing of the western maritime border by a fishing boat carrying 31 North Koreans on Saturday.

The South Korean military says that the fishing vessel crossed the Northern Limit Line (NLL) in waters northeast of Yeonpyeong Island in the Yellow Sea at around 11 a.m. Saturday and that the Navy has since escorted the boat to Incheon.

Thirty-one North Koreans, including eleven men and 20 women, were on the boat.

Military and intelligence officials in Seoul are attempting to determine why the North Koreans crossed the NLL.

Based on the findings so far, investigators believe the fishing crew most likely drifted across the NLL accidentally amid foggy weather, but the high number of women could also indicate a group defection.

Some of the North Koreans have reportedly expressed their intent to return to the North.