Along with South Korea.
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Many contentious issues confront China and Japan. Among the most pressing is their thirst for energy. Japan depends on imports for 99 percent of its oil and natural gas; coastal China is similarly bereft of resources. Thus, the offshore oil and gas fields under the East China Sea are attractive "domestic" sources of energy for both Beijing and Tokyo -- and both have laid claim to them. China argues that the entire East China Sea continental shelf, extending eastward nearly all the way to Okinawa, is a "natural prolongation" of the Chinese mainland. Japan has declared its boundary to be a median line between its undisputed territory and China -- a line that runs roughly 100 miles west of the Okinawa Trough, which lies undersea just west of Okinawa and is where the richest petroleum deposits in the area are believed to be concentrated.
http://www.foreignaffairs.org/20060301faessay85210/kent-e-calder/china-and-japan-s-simmering-rivalry.htmlsnip>
On August 16, a Russian patrol boat fired a warning shot at a Japanese crab fishing boat near a disputed chain of islands. The warning shot killed one of the Japanese crew, making him the latest casualty of World War II. The incident sparked the most recent diplomatic incident over the islands Japan calls its Northern Territories and Russia the southern Kurils. Recent years have seen increased economic integration between Russia and Japan, but the disputed islands have prevented the signing of a treaty to officially end WWII between the countries and are an obstacle to further cooperation.
Nearly two weeks after the killing, the diplomatic dispute continued as Russia claimed that 39 Japanese fishing boats entered the disputed waters in an act of deliberate provocation. The Russian foreign minister said that bilateral ties could be affected if Japan does not take "urgent, effective measures" to prevent another incident. While this diplomatic row will continue to play out in the coming weeks, it is unlikely to affect the increasing economic and geopolitical cooperation between Russia and Japan.
http://pinr.com/report.php?ac=view_report&report_id=549&language_id=1