The United States said Saturday it was “deeply concerned” and committed to defending Japan after China announced an air zone in the East China Sea that covers disputed islets. In a move that U.S. ally Japan branded as “very dangerous,” China said it was setting up an “air defense identification zone” over islands administered by Tokyo to “guard against potential air threats.” In similar statements, Secretary of State John Kerry and Secretary of Defense Chuck Hagel said that the United States was “deeply concerned” about the moves by China, which also scrambled jets to carry out a patrol in the...