The boat has been towed to a South Korean military port for investigation.

According to the Joint Chiefs of Staff, the wooden boat was first spotted about 5.5 kilometers above the Northern Limit Line, the de facto maritime border at around 10:15 p.m. on Saturday. It started moving down in a straight line to cross the NLL at 11:21 p.m.

The South Korean Navy that was keeping a watch immediately deployed a high-speed boat, a rigid-hulled inflatable boat and a patrol frigate to the scene.

“The North Korean crew said they lost their way and crossed the border by mistake,” a JCS official explained.

When South Korean Navy officers checked the boat and asked the three crew members whether they had come with the purpose of defecting, they reportedly denied it.

The three North Koreans were taken to a naval port in Yangyang, Gangwon Province, for investigation. The 10-meter-wooden boat was also towed.

The JCS said there were many fishing gears on the boat with squid in the storage cabin. A while towel was tied to its mast.

Not all North Korean fishing boats are brought to the South for investigation. But the fishing boat on Saturday was towed as there were some peculiar points that need to be clarified, the JCS official explained.

While the North Korea crew said they came into the South Korean sea space by mistake, they entered in a straight line, the JCS said. The tag on the boat also showed the boat is operated by the North Korean military, though further investigation is needed to confirm whether the fishermen are from the North Korean military.

The boat was the only vessel spotted around the NLL area at the time.

About 380 North Korean fishing boats have been expelled for illegally fishing below the NLL, from May 31 to July 14, according to the Defense Ministry. The number appears to have surged from last year’s 40, as shoals of squid have increased around the border line this year.