The Kuril Island conflict is a dispute between Japan and Russia over sovereignty over the most southern four of the Kuril Islands. The disputed islands are currently under Russian administration as part of the Sakhalin Oblast but are also claimed by Japan which refers to them as the Northern Territories (北方領土) or Southern Chishima (南千島). The disputed islands are:
The dispute results from an ambiguity over the Treaty of San Francisco. Under Article 2c), Japan renounces all right, title and claim to the Kuril Islands, and to that portion of Sakhalin and the islands adjacent to it over which Japan acquired sovereignty as a consequence of the Treaty of Portsmouth of 5 September 1905.
However in 1855, the Treaty of Commerce, Navigation and Delimitation (the Shimoda Treaty), which provides for an agreement on national boundaries between the two nations, was concluded. Article Two of the treaty states "Henceforth the boundary between the two nations shall lie between the islands of Etorofu and Uruppu. The whole of Etorofu shall belong to Japan; and the Kurile Islands, lying to the north of and including Uruppu, shall belong to Russia." Note that Kunashiri, Shikotan and Habomais Islands are not explicitly mentioned in the treaty.
See also: Foreign relations of Japan, Treaty of Saint Petersburg.
External link: Japan's Northern Territories (Japanese government website)