Russian President Vladimir Putin visited a disputed island close to Japan on Thursday prompting a strong condemnation from Tokyo, which said his actions had made any improvement of relations between the countries 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 seized by Moscow in the days after Japan’s surrender in World War Two. 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 Two, 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 Two. They also warned against re-militarisation 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 behaviour ​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.