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.
