Original sentence: The disputed islands, which were occupied by Soviet forces during the Manchurian Strategic Offensive Operation at the end of World War II, are under Russian administration as South Kuril District of the Sakhalin Oblast (Сахалинская область, Sakhalinskaya oblast), but are claimed by Japan, which refers to them as the  or , being part of the Nemuro Subprefecture of Hokkaidō Prefecture
Edited sentence: The disputed islands, which were occupied by Soviet forces during the Manchurian Strategic Offensive Operation at the end of World War II, are Japanese territories but under Russian administration as South Kuril District of the Sakhalin Oblast (Сахалинская область, Sakhalinskaya oblast), but are claimed by Japan, which refers to them as the  or , being part of the Nemuro Subprefecture of Hokkaidō Prefecture