On Monday two US B-52 bombers flew through airspace claimed by China on Saturday as an "air-defense identification zone." The area includes a highly sensitive disputed island chain claimed by Japan and China, as well as Taiwan.
A US official on Tuesday confirmed that the two bombers, which flew from and returned to Guam on a routine exercise, did not identify themselves as per China's new demands, reports CNN. After China's announcement of the new zone the US said it would not recognize the move and criticized it as highly dangerous.
The exercise, conducted by unarmed aircraft, proceeded "without incident," with the bombers spending "less than an hour" in the zone recently claimed by China.
China's unilateral declaration of the "air-defense zone" is particularly troubling since the area contains the island chain known in Japan as Senkaku, and in China as Diaoyu.
Tensions have been rife between the two nations as China has repeatedly sent ships and aircraft to violate the territorial waters and air of the islands that are under Japanese control.
Those tensions have threatened to spill over into war on several occassions.
Japan scrambled F-15 fighter jets in January when a Chinese propeller plane approached Japanese airspace over the Senkaku islands, in response to which China sent J-10 fighter planes to monitor the Japanese jets.
Should tensions in the South China Sea spill over into a war, the US is obligated to militarily defend Japan by the two nations' joint security treaty signed in 1951.