(CNN) -- Japan's military scrambled fighters Thursday after two Russian SU-27 jets entered Japanese airspace off Rishiri Island near the tip of Japan's northernmost Hokkaido Island, according to the country's Defense Ministry.
The Russian jets left Japanese airspace without incident after a little more than a minute, the ministry said.
The incident occurred near territory disputed by Japan and Russia since the end of World War II.
Japanese officials lodged an official protest with Russia over the incident, Japan's Kyodo news service reported.
Russian officials denied their jets entered Japanese airspace, the Russian Interfax news agency reported.
The incident is the first since 2008, Kyodo reported.
Japanese Prime Minister Shinzo Abe has made a priority of resolving the longstanding dispute with Russia over what it calls the Northern Territories and Russia calls the Kuril Islands, according to Japanese newspaper Asahi Shimbun.
Russia and Japan have squabbled over the islands -- Etorofu, Kunashiri, Shikotan and Habomai -- since the end of WWII, when Russian forces took over the islands, according to the Japanese Foreign Affairs Ministry. Because of the dispute, the two countries never signed a peace treaty following the war.