A pair of American B-52 bombers flew unannounced into a recently established Chinese no-fly zone in the East China Sea, in a direct rebuke of Beijing's asserted authority over the area.
The bombers, based out of Andersen Air Force Base in Guam, entered the contested airspace as part of a training operation dubbed Coal Lightning, according to The Wall Street Journal.
"The planes flew a pattern that included passing through the [Air Defense Identification Zone]," the official said.
"The flight was without incident," the official added.
Over the weekend, Chinese leaders instituted new rules for U.S. allied military aircraft operating in the skies above the Diaoyutai and Senkaku islands in the East China Sea.
U.S. and allied forces are required to identify themselves and their mission to Chinese forces before entering the no-fly zone, according to Beijing. The two B-52 bombers did not do so.
Defense Secretary Chuck HagelChuck HagelLobbying World The US just attacked Syria. So where's Congress? Senators tear into Marines on nude photo scandal MORE on Saturday said the new no-fly zone was another example of aggressive Chinese expansion that "increases the risk of misunderstanding and miscalculations" between Washington and China.
"The United States is conveying these concerns to China through diplomatic and military channels, and we are in close consultation with our allies and partners in the region, including Japan," Hagel said in a statement.
A majority of American operations flown in the area consist of intelligence, surveillance and reconnaissance operations and large-scale training missions with U.S allies.
The Diaoyutai and Senkaku islands in the East China Sea have frequently been a flashpoint between China and U.S. allies in the Pacific. The area had been considered international airspace.
Last August, the Pentagon began flying unmanned surveillance missions over the small Pacific island chains as part of a defense security agreement with Japan.
Former Defense Secretary Leon Panetta and Japanese Defense Minister Satoshi Morimoto agreed to the drone operations after a bilateral meeting in Washington.