Japan has dispatched a surveillance plane and a navy ship after spotting a Russian submarine off the coast of a southwestern island near Taiwan.

The Russian Kilo-class submarine was sighted just 50 kilometers (31 miles) south of Yonaguni Island, Japan’s westernmost territory just east of Taiwan, the Japanese Joint Staff said in a statement.

The submarine, accompanied by a Russian naval ship, was moving northeast between Yonaguni and the nearby island of Iriomote. It was the first sighting of a Russian submarine in those waters, the Joint Staff said.

It added that Japan’s Self-Defense Forces deployed a combat support ship and a P-3 survey aircraft for warning and reconnaissance operations. There was no breach of Japan’s territorial waters by the Russian warships, it said.