A Russian air force bomber briefly violated Japanese airspace over the uninhabited island of Sofugan just south of Tokyo on Saturday, the Foreign Ministry said.
The three-minute flyby over Sofugan in the Izu island chain by a Tupolev 95 ended after it was warned off by Japanese fighter jets, said Foreign Ministry official Kotaro Otsuki.
The ministry immediately lodged a protest with the Russian Embassy in Tokyo and demanded an explanation, Otsuki said.
A switchboard operator at the Russian Embassy said no one was available to comment Saturday.
The Maritime Self-Defense Force scrambled 22 fighter jets, including F-15s and two airborne warning and control aircraft, a Defense Ministry official said on condition of anonymity, citing protocol.
Japan held a rally Thursday to demand the return of a disputed island chain Russia seized in the closing days of World War II. The capture of the four islands has kept the two countries from signing a formal peace treaty.
Japan holds a rally every Feb. 7, the anniversary of an 1855 Japan-Russian friendship treaty that gave Japan possession of the islands.