Japan’s Foreign Ministry, in its annual diplomacy report “Blue Book” reportedly labeled the southern part of the Kuril Islands as “illegally occupied” by Russia. An official publication of the document is expected in the coming days, Kyodo news agency reported. Known in Japan as the Northern Territories this is the first time since 2003 that Japan has reportedly used this type of language to describe the Russian occupation of the islands.

The islands have been under Russian administration since their 1945 Invasion by the Soviet Union at the end of World War II. Japan claims the four southernmost islands, including two of the three largest ones (Iturup and Kunashir), as part of its territory, as well as Shikotan and the Habomai islets, which has led to the ongoing Kuril Islands dispute.

The move follows the Russian decision on refusing to negotiate a peace treaty with Japan, halting visa-free travel for Japanese citizens to the Southern Kuril Islands, and withdrawing from dialogue with Japan on establishing joint economic activities on the archipelago, reported Russian news outlet, Sputnik.