Japan's Defense Ministry says four airplanes apparently belonging to the Russian military were observed flying directly toward Japan's airspace off its northern main island of Hokkaido on Tuesday night.

Ministry officials say the Self-Defense Forces described the move as rare in recent years.

They say the aircraft were flying over the Sea of Japan toward the west of Hokkaido. Two of them turned around before reaching Japanese territorial airspace, and the other two changed course northward in the direction of Sakhalin.

Japan's Air Self-Defense Force scrambled its fighter jets in response. The officials say there was no violation of the country's territorial airspace.

The officials say there have not been any cases in recent years of Russian military aircraft flying directly toward Japanese territorial airspace.

They are analyzing the purpose of the unusual move by the Russian military while staying alert and monitoring the skies.