Russian President Vladimir Putin visited a disputed island near Japan Thursday, drawing a strong reaction from Tokyo, which said the move made improving relations between the two countries more difficult.
The island, known in Russia as Iturup and in Japan as Etorofu, is one of four in the Kuril chain, close to Japan's main islands, that Moscow seized in the days after Japan's surrender in World War II.
Tokyo has maintained its claim to them, making their return a condition for concluding a formal peace treaty that would unlock closer economic ties.
It "hurts the feelings of the Japanese people and is absolutely unacceptable," Prime Minister Sanae Takaichi said in a televised statement.
"We hope that the Russian side will take the seriousness of this matter fully to heart," she added.
Ties between Moscow and Tokyo soured after Putin ordered the full-scale invasion of Ukraine in 2022. Japan joined other nations in condemning the attack and imposing sanctions on Russia.
Putin's visit to the island comes two days before Japan marks 81 years since its surrender ended World War II and a day after North Korea fired a missile into the sea separating it from Japan ahead of major joint military exercises by Seoul and Washington.
Dmitry Medvedev was the first Russian leader to visit the disputed territory in 2010.
On Thursday, the Russian and Chinese ambassadors to Japan, Nikolai Nozdrev and Chinese Ambassador Wu Jianghao, issued a joint statement pledging to oppose attempts to revise the results of World War II.
They also warned against remilitarization in the Asia-Pacific, language that echoes Moscow's rejection of Japan's claim to the islands.
On the trip, which state news agency TASS described as Putin's first to the island chain, he visited the Yasny fish-processing plant on the island, after overseeing navy drills in Russia's Far East.
Vesti TV channel images showed Putin in a dark suit, beside two large tuna and a halibut laid out on a table, as two officials spoke about fishing and the migratory behavior of fish. He also stopped to try local fish roe.
"What lovely weather you have there, just like a resort!" Putin told a group of locals.
