TOKYO—U.S. Secretary of Defense Ash Carter said the U.S. was concerned by China’s land reclamation efforts in the South China Sea and by the possibility that construction there has a military dimension.

Speaking to reporters after meeting Japanese Defense Minister Gen Nakatani on Wednesday, Mr. Carter said the U.S. prioritizes stability in the Asia-Pacific and wants to ensure “no changes in the status quo are made coercively and that territorial disputes, which are long-standing, are not militarized.”

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