A Chinese navy vessel has seized an unmanned US underwater drone that was in international waters. The vessel was seized in the South China Sea just as USNS Bowditch, an oceanographic survey ship, was about to retrieve it. A Chinese naval vessel that had been shadowing the Bowditch dispatched a small boat which seized the drone.

The US Navy received no answer when it said the drone was American property. The Chinese eventually responded simply to say they were returning to their own operation, a US Defence official told CNN.

The incident occured about 50 miles (80km) north-west of Subic Bay in the South China Sea.

"It was taken" by China, a US official told the media. "The UUV [unmanned underwater vehicle] was lawfully conducting a military survey in the waters of the South China Sea," the official said.

"It's a sovereign immune vessel, clearly marked in English not to be removed from the water – that it was US property."

The incident comes after a series of spats between US President-elect Donald Trump and Beijing caused by Trump breaking decades of diplomatic protocol by speaking to the leader of Taiwan.

Meanwhile, China's first aircraft carrier has conducted live-fire drills for the first time, the defence ministry has said. The exercise took place in recent days in the Bohai Sea, near the Korean peninsula.

Ten vessels and 10 aircraft engaged in air-to-air, air-to-sea and sea-to-air combat drills, state media reported. The exercise comes as concerns grow over China's increasing military presence in the South China Sea.

The exercise comes the day after the Asia Maritime Transparency Initiative (AMTI) released new photographs it said showed "significant" Chinese military defences on artificial islands China has built in the South China Sea.

The rising tension comes amid concerns the president-elect Trump is poised to pivot on American policy towards China and might revisit the issue of Taiwan's independence as an opening gambit in trade negotiations with Beijing.

"The calculating businessman might feel shrewd about seizing China's fate by the throat through the Taiwan question," responded China's state-run Global Times newspaper, a mouthpiece for hard-right nationalists. "However, the truth is this inexperienced president-elect probably has no knowledge of what he's talking about." If Trump tries to change Taiwan's status, China, might well "offer support, even military assistance to U.S. foes," it said.

According to Newsweek (IBTimes UK's sister publication) Trump's fans in Washington's right wing think tanks scoffed at such threats and cheered what they saw as an overdue "punch in the face" to China, as a soon-to-be-retired intelligence officer put it to a Newsweek reporter at a December holiday party. If China responded militarily, a Heritage Foundation official said, "We could cream them."