A look at the website of Japan's Foreign Ministry shows that there are considerable differences in terms of the urgency and persuasiveness of Japan's international territorial disputes in areas to the north, east and west.
To the east of Japan lie the so-called "Northern Territories" or Kuril Islands, which are subject to a dispute with Russia, and to the west the Senkaku Islands, which are disputed by China, which calls them Diaoyutai. To the north of Japan lie Korea's Dokdo Islets, which Japan claims.
Japan's claim to the Senkaku Islands is the strongest. The website classifies Dokdo and the "Northern Territories" as areas of territorial dispute, but not the Senkaku Islands. Instead, it mentions them in a separate section entitled "recent Japan-China relations" -- in other words, Japan does not even recognize the area as disputed territory. And the content devoted to the Senkaku Islands amounts to just half of page in length and merely states that "the government of Japan made a Cabinet decision on Jan. 14, 1895 to erect a marker on the Islands to formally incorporate the Senkaku Islands into the territory of Japan" and that "it was not until the latter half of 1970, when the question of the development of petroleum resources on the continental shelf of the East China Sea came to the surface, that the government of China and Taiwan authorities began to raise questions" about them.
Next in importance are the Northern Territories. The website says Japanese people were the first to inhabit the four islands, while Japan and Russia signed a treaty recognizing them as Japanese territory in 1855. Soviet troops occupied them after World War II. Tokyo says Russia must return them to Japan. Since Russia has offered to return two of the four islands, so Moscow appears to acknowledge Japan's claims to some extent.
But matters are different when it comes to Dokdo. Most of the text on the website focuses on the historical timing of the recognition of the existence of the islets, Korea's position and Japan's response. It contains a reference to the so-called "Syngman Rhee Line" drawn by the former Korean president in 1952, which established Korea's maritime boundaries encompassing Dokdo and claims it violated international law. While more than half of the material on Dokdo is responses to Korea's claims, the parts about the Senkaku Islands and the Northern Territories do not even feature rudimentary information on other side's claims.
Korean government officials say that a considerable number of Japanese politicians and senior government officials believe that China and Russia have weakly substantiated claims to the Senkaku Islands and the Northern Territories, but the Korean government appears to have a historical basis to lay claim to Dokdo.
From Japan's perspective, it controls the Senkaku Islands, so they are not disputed territory. The Kuril Islands are under Russian control, but it believes they clearly belong to Japan from a historical perspective and must be returned. But the Dokdo islets are said to be "illegally occupied" by Korea and must first of all be established in international eyes as disputed territory. This is why Japan continues to make provocative comments about the Korean islets.