TOKYO (AP) — The head of the U.S. Indo-Pacific Command said Monday he is “very concerned” about increased joint military actions by China and Russia in the region.

Adm. John C. Aquilino spoke in Tokyo as another regional concern, North Korea, conducted its latest intercontinental ballistic missile test, underscoring the advancement of its capabilities.

Aquilino is meeting with Japanese defense officials ahead of a joint exercise, Keen Edge 24, early next year.

He urged China to stop escalating maritime confrontations with its neighbors, and said its increasing military activity with Russia is a serious concern during Moscow’s war in Ukraine.

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“I view it as far beyond the marriage of convenience at this point in time” he said. “If you tied DPRK (North Korea) into that, the Russia-DPRK cooperation, and the fact that the only partner of the DPRK prior to that was (China), that’s just a bad neighborhood and bad group to be in,” Aquilino said.

North Korea has been pushing to expand cooperation with Russia and China. There have been concerns that the North has supplied missiles and other ammunition to Russia to support its war in Ukraine, in exchange for obtaining Russian missile technology.

Chinese and Russian bombers had a joint flight last week over the East China Sea to the waters between Japan and the Korean Peninsula, causing Japanese fighter jets to scramble against them, according to Japan’s Defense Ministry.

Japan has territorial disputes with China over the Japanese-controlled East China Sea islands which Beijing also claims. It considers China a threat to national security and is in the process of a rapid military buildup.

Japan is particularly concerned about China’s increased joint activity with Russia’s military around the Japanese coast.

China has growing tensions with other neighbors.

Standoffs between China and the Philippines over a number of disputed offshore areas in the South China Sea have escalated this year. The United States has warned China that it is obligated to defend the Philippines, its treaty ally, if Filipino forces come under attack. China has warned the U.S. to stay away from what it calls a purely Asian dispute.

China also activated sonar in waters where an Australian ship had divers working.

But China’s flight and maritime close encounters with U.S. warplanes and ships have stopped since U.S. President Joe Biden and China’s Xi Jinping agreed in November to stabilize their relationship and re-establish military communication.

But Aquilino’s requested talks with his Chinese counterpart have been pending for three years, and he is waiting for China to respond to his renewed request.

“No reply yet,” he said, other than the Chinese embassy saying they have to work out the technology to set up the call.