Japan expressed "serious concerns" on Wednesday after Chinese and Russian heavy bombers conducted rare joint flight operations around Japan the previous day as leaders of "the Quad" grouping met in Tokyo.

The Defense Ministry said it had scrambled fighter jets Tuesday in response to the operations that included a total of six Chinese and Russian bombers that made a joint flight through the Sea of Japan, East China Sea and into the Pacific Ocean. The warplanes did not enter Japanese territorial airspace.

Chief Cabinet Secretary Hirokazu Matsuno, the government's top spokesman, said during a news conference broadcast online on Wednesday that Tokyo could not overlook actions such as flights that "increase tensions in East Asia" when Moscow was continuing with its bloody war in Ukraine.

Matsuno said Japan had protested the move with both Beijing and Moscow.

Speaking Tuesday night, Defense Minister Nobuo Kishi said the move was especially "provocative," given that Tokyo was hosting the summit of leaders from the Quad nations — the United States, India, Australia and Japan.

"We believe the fact that this action was taken during the Quad summit makes it more provocative than in the past," he said, adding that it had been the fourth such joint long-distance flight since November.

A statement released by the ministry said a Russian intelligence-gathering aircraft had also flown off northern Hokkaido to the Noto Peninsula in Ishikawa Prefecture the same day.

Both the Russian and Chinese sides also confirmed the flight, with the Defense Ministry in Moscow saying in a statement that the “patrol” had lasted 13 hours.

In a statement on its website, the Chinese Defense Ministry said the flight, the first since Russia's invasion of Ukraine, was the fourth iteration of an annual military exercise.

At Tuesday's Quad meeting, divisions on views of Russia’s invasion of Ukraine — which China has implicitly backed — were clearly visible. While the leaders touted unity, the joint statement that warned against attempts to "change the status quo by force" did not directly refer to Russia or China.