BEIJING - China said a US spy plane entered a no-fly zone used by the Chinese military for live-fire drills, branding it an act of provocation, state media said Tuesday.

The U-2 reconnaissance jet's flight over an area in northern China violated safety rules between the two nations, Xinhua reported, citing Chinese defense ministry spokesman Wu Qian.

"The US action could easily have resulted in misjudgments and even accidents," said the report, adding "that the move was an obvious provocation."

"China firmly opposes such provocative actions and has lodged solemn representations with the US side."

Beijing's anger comes as US and Chinese relations have deteriorated to historic lows, with confrontations simmering on trade, military and political matters.

On the military front, US naval forces regularly conduct operations near Taiwan and in the South China Sea, effectively challenging China's territorial claims.