A Chinese aircraft carrier completed a series of combat exercises in the Yellow Sea, the Associated Press reported early Saturday.

The move comes amid increased tensions between the U.S. and China in the South China Sea, which were exacerbated last week when China seized an unmanned underwater Navy drone.

China’s Defense Ministry announced late Friday that the Liaoning carrier group conducted fighter launch, recovery and air combat exercises in the Yellow Sea in recent days.

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The ministry said the group will soon “conduct scheduled cross-sea training and tests.” It was not immediately clear what that meant, Chinese media speculated that it could be a move toward the contested South China Sea.

China claims control of nearly the entire sea and accuses the U.S. military of acting too provocatively in the area.

China’s increased aggression toward the U.S. is thought to be linked to Trump’s decision to take a phone call from Taiwanese President Tsai Ing-wen last month, breaking decades of diplomatic protocol.

No U.S. president or president-elect had spoken with a leader of Taiwan since the U.S. normalized relations with China in 1979. China considers Taiwan a breakaway province, not a separate country.