Beijing insists it has no hostile intent, but its sabre-rattling in the busy South China Sea, and around Taiwan, has touched a nerve in the region and in Washington.

In a “freedom of navigation” operation on Friday, a US Navy destroyer came within 12 nautical miles of an artificial island China has built in the South China Sea, provoking condemnation from Beijing, which claims most of the strategic waterway.

Zeng said it was not possible to single out any one trigger for the air force drills, saying there could be a number of political or diplomatic motivations behind such an unusually large mission.