Japan has strongly protested Russian President Vladimir Putin’s first-ever visit to the disputed Kuril Islands, escalating tensions between Tokyo and Moscow over the long-running territorial dispute.

Putin visited Iturup, known as Etorofu in Japan, the largest of the four southernmost islands claimed by both countries. During his visit, he toured a fish-processing facility, visited a secondary school and hospital, and met with Sakhalin Region Governor Valery Limarenko.

Japan’s Foreign Minister Toshimitsu Motegi condemned the visit and reaffirmed Tokyo’s claim to the islands.

“The Northern Territories, including Etorofu Island, are Japan’s inherent territory both historically and from the perspective of international law,” Motegi said, adding that Japan “strongly protests” Putin’s visit.

The dispute involves four islands, Iturup, Kunashir, Shikotan and the Habomai islets — located northeast of Japan’s Hokkaido.

The Soviet Union seized the islands in the final days of World War II in August 1945 and expelled about 17,000 Japanese residents. Japan refers to the islands as the Northern Territories and maintains that their seizure was unlawful.

The unresolved dispute has been a major obstacle to relations between the two countries and has prevented Moscow and Tokyo from signing a formal post-war peace treaty.

Although senior Russian officials have previously visited the islands, including former President Dmitry Medvedev in 2010 and then-Prime Minister Mikhail Mishustin in 2021, Putin’s visit marks his first personal trip to the disputed territory since becoming president.

Relations between Russia and Japan have deteriorated significantly since Moscow launched its full-scale invasion of Ukraine in 2022.

Japan joined other G7 nations in imposing sanctions on Russia and providing financial and other forms of support to Ukraine. Moscow subsequently suspended peace treaty negotiations with Tokyo and halted several joint economic projects involving the disputed islands.

Before travelling to Iturup, Putin visited neighbouring Sakhalin, where he discussed security along Russia’s eastern borders and criticised Japan’s sanctions against Moscow.

The visit is likely to further strain already fragile relations between the two countries and reinforce Moscow’s position that the disputed islands are under Russian sovereignty.

The Kuril Islands are also strategically important to Russia because of their military infrastructure, including coastal defence missile systems and airfields that help Moscow monitor and control key maritime routes in the North Pacific.