Three South Korean fishing vessels are returning home after being briefly detained by the North Korean coast guard on Sunday.

The squid fishing boats were seized earlier in the day in waters west of Songjin in the North’s Hamgyong Province.

South Korean authorities say the boats were released later in the afternoon after investigation by North Korean authorities.

It's not known yet why the boats were detained, but South Korean officials suspect they may have either strayed into the North's exclusive economic zone at night in pursuit of squid or miscalculated their course.