China has filed “stern representations” against the United States after the nation sent spy planes in China’s no-fly zone during a live-fire military drill. It has not only pushed Beijing to protest but also increased the chances of armed conflict, further straining the already sour relationship between the U.S. and China.

For weeks, there has been an increase in U.S. activity in the region, which includes the deployment of many military jets and vessels to keep a close watch on Chinese activity. According to Beijing-based think tank South China Sea Probing Initiative, a U.S. air force reconnaissance aircraft RC-135S flew across the South China Sea August 26, though it appeared to be on a transfer, rather than on a reconnaissance mission.

But Chinese defence ministry spokesman Wu Qian shared that a U-2 reconnaissance jet flew over the no-fly zone in the PLA’s northern military region without permission. It happened while the live-fire drills were taking place.

“It seriously interfered in normal exercise activities. It seriously violated the code of safe behaviour for air and sea between China and the US and international norms. It easily leads to misjudgment, or could even cause accidents in the sea and air,” Wu said. “The move was an obvious provocation. China firmly opposes such provocative actions and has lodged solemn representations with the U.S. side.”

“It would be a huge trouble if the plane was shot in the live-fire naval exercise. Frictions are bound to occur if the distance is not well kept,” said Hu Bo, director of the South China Sea Probing Initiative. 

But as per Liu Weidong, a U.S. affairs expert from the Chinese Academy of Social Sciences, the U.S. flew their spy plane over a no-fly zone, not with the intention to attack or snoop on China but to send a different message. 

“By flying the U-2 into China's no-fly zone, the U.S. is telling China that the game rules are not decided by Beijing, and ‘I can come if I want’,” Weidong said. “But the plane is not the most advanced reconnaissance aircraft, and not an attacking warplane either. And similar spying activities from the U.S. have happened many times already. I think this is more a political gesture, saying the US can do whatever they like without being constrained by Chinese military power.”

US Stealth Plane Tensions rise as US spy plane enters China’s no fly zone during live-fire naval drill. Photo by JACK GUEZ/AFP via Getty Images