BEIJING—China vowed to step up military cooperation with Russia, a day after the two countries’ first joint air patrol triggered a rare confrontation over the Sea of Japan and stoked U.S. concern about the intensifying partnership between Beijing and Moscow.

Releasing a new defense “white paper” Wednesday, China accused the U.S. of undermining regional stability by strengthening its alliances, and sharpened a warning that Beijing would use force, if necessary, to prevent Taiwan from declaring independence.

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