Putin visited the disputed island of Iturup: Japan protested.

Russian leader Vladimir Putin visited Iturup Island, part of the Kuril Islands, which Japan claims. Tokyo declared that it considers the island its territory and protested to Moscow.

The BBC reports this.

Putin visited Iturup the day before, becoming the first Kremlin leader to visit the Kuril Islands. During his trip, he visited the Yasny fish processing plant.

The Kuril Islands have been the subject of a territorial dispute between Russia and Japan for many years. After World War II, the Soviet Union established control over the archipelago, which is currently held by Russia.

Japan, in turn, claims sovereignty over the four southern Kuril Islands—Iturup, Kunashir, Shikotan, and the Habomai group. Tokyo calls them the Northern Territories.

The territorial dispute over the islands was one of the reasons why Russia and Japan have still not concluded a full-fledged peace treaty after World War II.

In response to Putin’s visit, the Japanese Foreign Minister protested. He stated that Iturup is an integral part of Japanese territory, both historically and under international law.

Earlier, Putin threatened Japan during military exercises .