Russian patrol planes this week entered airspace above the Sea of Japan where the United States and Japan were conducting joint military drills, causing a halt to part of the exercises, Japan's Sankei newspaper reported on Wednesday.
Japanese Chief Cabinet Secretary Yoshito Sengoku confirmed that the Russian planes had entered the airspace on Monday, prompting fighter planes from the US-Japan side to scramble, but did not give details.
Ties between Japan and Russia have been strained since Russian President Dmitry Medvedev's visit in November to one of four islands claimed by both countries, infuriating Tokyo.
Japanese Foreign Minister Seiji Maehara viewed the islands from a plane on Saturday. The Sankei speculated that the Russian action could have been in response to the move.
Japan's relations with China were also strained after Tokyo detained a Chinese fishing boat captain whose trawler collided with Japanese patrol boats near disputed islands in the East China Sea. The captain was released and the Asian neighbours have since sought to repair relations, but mutual mistrust runs deep.
Japan, the United States and South Korea on Monday called on Beijing to do more to rein in North Korea's belligerence after Pyongyang's shelling of a South Korean island killed four people on Nov 23, causing regional tensions to spike.