Japan’s two biggest airlines have defied the identification order since Wednesday at the request of the Japanese government.
Although there are risks of a confrontation in the zone, US and Chinese military officials have stepped up communication with each other in recent years and are in regular contact to avoid accidental clashes.
US Vice President Joe Biden will be visiting China, Japan and South Korea next week, and will try to ease tension over the issue, senior US administration officials said.
“We decline to comment on Chinese flights, but the United States will continue to partner with our allies and operate in the area as normal,” a Pentagon spokesman said.
China’s Ministry of National Defense has said that it was aware of the US, Japanese and South Korean military aircraft in the zone and had tracked them all.
In a show of support to the military, Chinese President Xi Jinping (習近平) visited a base in Jinan in eastern China, where he said “military training is critical to beef up the PLA’s [People’s Liberation Army] war capacities,” Xinhua reported.
Xi did not make direct mention of the East China Sea air defense zone.