The South Korean military on Thursday night rescued seven North Koreans from three boats that had apparently strayed into southern waters across the western inter-Korean sea border, the Joint Chiefs of Staff said Friday.

Two of the vessels sank near Baengnyeongdo, one of the five northwestern border islands, while the other was sent back to the North, officials said.

At around 7:12 p.m. and 9:30 p.m., South Korean patrol ships rescued four crew members from the two vessels. When they were found, the sailors were desperately removing water while their boats were sinking.

The four North Koreans were sent to the investigative authorities to find out whether they wanted to defect to the South and how they ended up in South Korean waters.

“Visibility at the time was very poor and the currents were moving from the North to the South at the time. The authorities are now investigating them to find out how they came here,” said JCS spokesman Col. Lee Bung-woo in a press briefing.

At around 11:35 p.m., another North Korean vessel carrying three people was spotted drifting after straying into the South.

As they showed no intention of taking asylum in the South, the South Korean military gave them fuel and sent them back to the North at around 2:38 a.m. on Friday based on “humanitarian principles,” JCS officials said.

On May 12, the South Korean military also found one vessel from the North drifting in South Korean territory. The ship carrying four North Koreans was sent back to the North on the same day, officials said.

By Song Sang-ho (sshluck@heraldcorp.com)