Two Chinese coast guard ships briefly entered Japanese waters Saturday around two islands off Kyushu, in the first confirmed entry by Chinese government vessels into the area, the Japan Coast Guard said.

Under the U.N. Convention on the Law of the Sea, vessels of every country have the right to sail through territorial seas as long as they do not harm the safety of the countries concerned.

The Japan Coast Guard requested the ships exit from the territorial waters, though it has not made it clear whether it considered their presence an intrusion into territorial waters.

According to the coast guard, it was notified by the Defense Ministry that one Chinese coast guard ship entered territorial waters near the southern tip of Tsushima Island around 11:50 a.m.

The ship exited the waters around 12:20 p.m. after the coast guard contacted the ship by radio and asked it to leave.

But the coast guard confirmed this ship and another Chinese vessel entered waters some 19 km north of Okinoshima Island around 3:50 p.m. The two exited the waters by shortly after 5 p.m., the coast guard said.

Tsushima Island is located about halfway between the southern tip of the Korean Peninsula and the northwest coast of Kyushu.

Chinese ships often enter Japanese territorial waters around the Senkaku Islands, in the East China Sea, a group of uninhabited islets controlled by Japan but claimed by Beijing.

Earlier this month, Okinoshima Island was added to UNESCO's World Heritage list. The whole area belongs to Munakata Taisha Shrine, and entrance by general citizens is tightly restricted.