Moscow said on Monday it had summoned the Japanese ambassador after Tokyo condemned President Vladimir Putin’s recent visit to Russia’s far-eastern Kuril Islands, which are also claimed by Japan.

Russian-Japanese relations have long been dogged by the contested islands, known in Japan as the Northern Territories and seized by the Soviet Union in 1945.

Moscow retaliated by summoning Japanese envoy Akira Muto.

Japanese officials had “crossed the line of decency” in criticising Putin’s trip, Foreign Minister Sergey Lavrov said on Monday.