A pair of U.S. military aircraft flew into China's newly established air defense identification zone in the East China Sea without informing Beijing, a U.S. Defense Department official said Tuesday.
"Last night we conducted a training exercise that had been long planned that involved two aircraft flying from Guam and returning to Guam," Col. Steve Warren, a Pentagon spokesman, told reporters.
The move came after China set up the zone that overlaps Japan's and asked the operators of airplanes flying in the area to submit flight plans in advance. The U.S. government criticized China for potentially destabilizing the security situation in East Asia.
The zone serves as national defense perimeters to judge whether fighters should be scrambled when foreign aircraft enter without prior notification. It surrounds a country's territorial airspace.
The aircraft conducted "normal flight operations that we have conducted in that region all the time," Warren said.
The Wall Street Journal said the aircraft that were flying in the air zone were B-52 bombers but Warren declined to confirm the type of the airplanes.
"We don't support efforts by any state to apply its air defense identification zone procedures to any foreign aircrafts not intending to enter its national airspace," Jen Psaki, spokeswoman at the State Department, told reporters.
The U.S. and Japanese governments strongly reacted to the Chinese move as the air zone covers the Japan-controlled Senkaku group of islets, an area where tensions between Japan and China are already increasing.
Secretary of Defense Chuck Hagel said Saturday, "This announcement by the People's Republic of China will not in any way change how the United States conducts military operations in the region."
China began to claim the Senkakus in the 1970s after studies indicated there may be vast oil reserves in the surrounding sea bed. China calls the islands Diaoyu and Taiwan also claims them, calling them Tiaoyutai.