Nobuo Kishi said Tokyo had expressed "grave concerns" to Russia and China over the flights, which took place while leaders from the United States, India, Australia and Japan held talks on regional security.

"Two Chinese bombers joined two Russian bombers in the Sea of Japan and made a joint flight to the East China Sea," Kishi told reporters.

"After that, a total of four aircraft, two presumed (new) Chinese bombers -- which replaced the two Chinese bombers -- and two Russian bombers, conducted a joint flight from the East China Sea to the Pacific Ocean."

Kishi said a Russian intelligence-gathering aircraft also flew off northern Hokkaido to the Noto Peninsula in central Japan on Tuesday, calling the moves especially "provocative" given the summit in Tokyo.

"We communicated through diplomatic routes our grave concerns from the perspective of our country's and the region's security," he said.

"As the international community responds to Russia's aggression against Ukraine, the fact that China took such action in collaboration with Russia, which is the aggressor, is cause for concern. It cannot be overlooked."