The Japanese government's position via Wikipedia > Although by the terms of Article (2c) of the 1951 San Francisco treaty, Japan renounced all rights to the Ku

The Japanese government's position via Wikipedia > Although by the terms of Article (2c) of the 1951 San Francisco treaty, Japan renounced all rights to the Kuril Islands, the treaty did not apply to the islands of Kunashiri, Etorofu, Shikotan and Habomai since they are not included in the Kuril Islands. Also, the Soviet Union did not sign the San Francisco treaty.