Japan on Thursday summoned Russian Ambassador to Japan Nikolay Stanislavovich Nozdrev to protest Russian President Vladimir Putin's visit to the disputed Iturup Island.
Foreign Minister Toshimitsu Motegi asked Nozdrev to convey Tokyo's protest to Moscow "as soon as possible," Kyodo News reported.
Putin visited Iturup earlier on Thursday during a trip to Russia's Far Eastern Sakhalin region, marking his first visit to the island chain off Hokkaido.
Long-running territorial dispute
Japan maintains that the Northern Territories of Iturup, Kunashiri, Shikotan and the Habomai islet group were "illegally" seized by the Soviet Union shortly after Japan surrendered in World War II on August 15 1945.
Russia, which refers to the islands as the Southern Kurils, maintains that the seizure was legitimate.
The territorial dispute has prevented Japan and Russia from signing a post-World War II peace treaty.
Tensions between the two countries have also deepened in recent years as Japan has imposed sanctions on Moscow over Russo-Ukrainian war.
