The Defense Ministry said Saturday that a foreign submarine headed west underwater in a contiguous zone northeast of Amami Oshima Island, in Kagoshima Prefecture, on Thursday afternoon.

Maritime Self-Defense Force destroyers and patrol aircraft monitored the submarine, which was traveling west outside a contiguous zone west of the prefecture's Yokoate Island on Saturday morning, according to the ministry.

The vessel passed through a narrow strip of waters between the prefecture's Tokara island chain and Amami Oshima without surfacing, according to the ministry.