Japan says two Russian fighter jets briefly entered Japanese airspace near the northern island of Hokkaido on Thursday, prompting Japan's air force to scramble fighter jets in response.
Tokyo lodged a protest with Moscow but Russia has denied that its jets had entered Japanese airspace. The incident comes amid a 60-year old feud between the two countries over northern territories. Japan's prime minister is now seeking a solution to the dispute.
The Japanese prime minister, who has taken an assertive stance on disputed territories since returning to office in late December, pledged Thursday to resolve a lingering islands dispute with Russia.
The decades-old impasse has meant the two countries have technically remained in a state of war since 1945.
Japan claims four islands in the northwestern Pacific. The closest is just several km from the northernmost point of Hokkaido and some 1,000 km to the south of Kamchatka peninsula on the Russian mainland.
Prime Minister Shinzo Abe spoke briefly to thousands of people at an annual rally in Tokyo dedicated to the return of the islands.
Abe says negotiations with Moscow are ongoing with the aim of settling the ownership question so a peace treaty can be signed with Russia. He expresses "strong hope" progress will be made and the dispute can finally be resolved.
The Soviet military invaded the southern part of Sakhalin and the Kuril islands within days of declaring war against Japan in August of 1945. Japan surrendered on August 15, bringing to an end the Second World War. The Japanese civilians living on the islands were expelled.
Japan has since contended that Soviet troops continued the August 1945 offensive against its forces even after the Imperial Japanese Army surrendered.
Japan says the unresolved territorial issue still prevents it from concluding a peace treaty with Russia.
Japan had been awarded a portion of Sakhalin as part of the Treaty of Portsmouth in 1905 after Japanese forces won a seven-month war with Russia.
Japan began colonizing the Kuril islands in the late 19th century. The ongoing dispute involves four of the chain's 18 islands.
Russia has been strengthening its military presence in the Kurils in recent years and visits by Russian leaders to the disputed islands have prompted strong criticism from Tokyo.
Moscow considers the islands claimed by Japan to be an integral part of the Russian Federation.
The Russians have proposed joint use of the disputed territory, which has potentially lucrative onshore and offshore mineral resources.
Leaders of both countries, in recent years, have jointly expressed a desire to solve the dispute through talks.