President Obama speaks at a joint news conference with Japan's Prime Minister Shinzo Abe in Tokyo on Thursday. Obama reinforced the U.S.-Japan security commitment. Junko Kimura-Matsumoto/AP hide caption

itoggle caption Junko Kimura-Matsumoto/AP

A ceremony is held to mark a new patrol vessel in service for China's marine surveillance in Zhoushan, east China's Zhejiang Province, last month. Shen Lei/Xinhua/Landov hide caption

itoggle caption Shen Lei/Xinhua/Landov

Concerns over China's air defense claims led Secretary of Defense Chuck Hagel to call Japan's defense minister Wednesday. Here, a man makes a call near a replica of a Chinese fighter jet displayed in Beijing Wednesday. Ng Han Guan/AP hide caption

itoggle caption Ng Han Guan/AP

Two U.S. B-52s, like the one shown here, have flown through an area that China says is within its air defense zone. China's announcement has irked its neighbors and the U.S. and Japan say they won't abide by it. Andy Rain /EPA/Landov hide caption

itoggle caption Andy Rain /EPA/Landov