The Japanese government on Thursday sent a strong protest to Moscow regarding Russian President Vladimir Putin's visit to the Kuril Islands. This is the first visit by a Russian leader to the archipelago, which Japan considers part of its territory. The territorial dispute over the southern part of the Kuril Islands remains one of the main reasons why Russia and Japan have not concluded an official peace treaty since the end of World War II. Tokyo claims the so-called Northern Territories, which include the islands of Iturup, Kunashir, Shikotan, and Habomai. The Japanese side refers to the bilateral Treaty of Commerce and Navigation of 1855. Moscow, in turn, asserts that Russia's sovereignty over the Southern Kuril Islands is not subject to revision. Putin's visit took place after his trip to Sakhalin. There, the Russian president observed naval maneuvers and participated in a meeting focused on security issues along the country's eastern borders. For Japan, the Russian president's trip has not only symbolic but also political significance. Any official visits by Russian leaders to the disputed islands traditionally provoke a sharp reaction from Tokyo. In a statement, Japanese Foreign Minister Toshimitsu Motegi said that the Northern Territories are an integral part of Japan "from a historical perspective and in accordance with international law," therefore the Japanese government expresses a strong protest regarding the visit. Relations between Moscow and Tokyo have further complicated since the onset of Russia's full-scale war against Ukraine. Japan joined the sanctions against Russia, after which bilateral dialogue became even more strained. This is not the first time that visits by Russian leaders to the disputed islands have provoked protests from Japan. In 2010, Dmitry Medvedev became the first Russian leader to visit the Kuril Islands and subsequently visited them multiple times while serving as prime minister. Vladimir Putin's visit once again highlighted that the territorial dispute between Russia and Japan remains unresolved and continues to affect the relations between the two countries.