Tokyo claimed on Thursday that Russian fighter jets had violated Japanese air space near the northern island of Hokkaido, adding more tension to a long-simmering conflict between the two countries over an island group.
The BBC reports that Japan quickly scrambled its own aircraft after detecting the Russian planes, while Russia denies the incursion.
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Japan had lodged a protest, according to its Foreign Ministry, Reuters reports, and noted that the incursion was the first such incident in 5 years.
Japan and Russia have been at odds over a disputed island group off Hokkaido known to the Japanese as the Northern Territories, and to the Russians as the Southern Kuriles, since the end of World War II. It's prevented the two countries from formally delcaring peace.
The timing of the latest incursion was unfortunate, Reuters notes: Thursday is traditionally a day when the Japanese protest for the return of the islands to Japan.
Japanese Prime Minister Shinzo Abe and Russian Prime Minister Vladimir Putin agreed in December to restart talks on a peace treaty between the two nations, which has been hampered by the island controversy since WWII, says the BBC.
China and Japan have also been noisily scuffling over another group of disputed islands, known as the Diaoyus to the Chinese, and the Senkakus to the Japanese.
Japanese officials claimed this week that a Chinese warship pointed its radar at Japanese military targets, wrote the Sydney Morning Herald.