"We express our concern in relation to the statements by [the Russian] defense minister. Possible strengthening of the Russian military infrastructure on four northern islands [South Kuril Islands] contradicts the stance of our government," Suga said at a press conference.
Tokyo is set to closely monitor Russia’s activities in the region, he added.
The Kuril Islands are the subject of the long-standing territorial dispute between Russia and Japan. Japan lays claims to Kunashiri, Etorofu, Shikotan islands and the Habomai group of islets dividing the Sea of Okhotsk from the Pacific Ocean. The territorial dispute has prevented Russia and Japan from signing a peace treaty after World War II.