Japanese Defense Minister Kishi Nobuo has expressed serious concern over joint flights earlier this month by Chinese and Russian bombers near Japan.
Japan's Defense Ministry says two aircraft from each country flew over the Sea of Japan and the East China Sea before heading toward the Pacific Ocean on Friday.
The ministry says the aircraft passed over waters between the main island of Okinawa and Miyako Island in southwestern Japan.
The disclosure marked the third time since last December that the Japan's Defense Ministry has made public information about Chinese and Russian joint flights.
Kishi said on Tuesday that repeated military exercises by China and Russia can be regarded as demonstrative action toward Japan. He said the possibility cannot be ruled out that they will deepen their military coordination.
Kishi expressed grave concern, noting that China and Russia's moves clearly indicate the security situation surrounding Japan is growing more severe.
He added that Japan will continue its strict warning and surveillance activities, and make every effort to substantially strengthen its defense capabilities.