Satellite photos taken in July show China appears to have built reinforced aircraft hangars on disputed islands in the South China Sea.
The images, taken by the Center for Strategic and International Studies, show the artificial enhanced reefs now have room for Chinese fighter jets.
The United States has repeatedly urged claimants not to militarize their holdings in the South China Sea.
States Department spokesperson Elizabeth Trudeau said all sides in the dispute should seek a diplomatic resolution.
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