Chinese warplanes and naval ships “tailed and monitored” an American destroyer as it sailed through the Taiwan Strait Saturday.

The US Navy said the guided missile destroyer USS Mustin had conducted “a routine Taiwan Strait transit Dec. 19 in accordance with international law.”

“The ship’s transit through the Taiwan Strait demonstrates the US commitment to a free and open Indo-Pacific,” the Navy statement said.

But China accused the US of provocation, Reuters reported. Such missions “deliberately raise the temperature of the Taiwan issue, as they fear calm in the Taiwan Strait, and send flirtatious glances to Taiwan independence forces, seriously jeopardizing peace and stability in the strait,” the Chinese military said.

China opposes any military relationship between the US and Taiwan.

It was the 12th time this year the US Navy sent a ship through the strait.

In Taipei, Taiwan’s Defense Ministry said it monitored the Mustin’s movements, and that “the situation was as normal.”

Beijing, which sees the island as a breakaway province, is worried that Taiwan plans to formally declare independence.

Taiwan President Tsai Ing-wen says Taiwan is already an independent country called the Republic of China. She has built up Taiwan’s armed forces as China has increased its military activity near the island.

Earlier this year, China sent fighter jets across the Taiwan Strait’s median line, an unofficial buffer.