China’s military has carried out its first ever live-fire drills using an aircraft carrier and fighters in the northeastern Bohai Sea close to Korea, state media said.

China’s growing military presence in the disputed South China Sea has fueled concern, with the United States criticizing its militarization of maritime outposts and holding regular air and naval patrols to ensure freedom of navigation.

No other country has claims in China’s busy waterway of the Bohai Sea, but the drills come amid new tension over self-ruled Taiwan, following U.S. President-elect Donald Trump’s recent telephone call with the island’s president that upset Beijing.

Ten vessels and 10 aircraft engaged in air-to-air, air-to-sea and sea-to-air combat drills that featured guided missiles, state broadcaster Chinese Central Television reported late on Thursday.

“This is the first time an aircraft carrier squadron has performed drills with live ammunition and real troops,” it said.

China’s Soviet-built Liaoning aircraft carrier and a formation of warships carried out aerial interception, anti-aircraft and anti-missile drills, in which Shenyang J-15 fighter jets carrying live missiles also participated, CCTV said.

It broadcast images of fighter jets taking off from the carrier, firing missiles and destroying a target at sea.

The Liaoning has participated in previous military exercises, including some in the South China Sea, but the country is still years off from perfecting carrier operations similar to those the United States has practiced for decades.

On Wednesday, a U.S. think tank said China had been installing anti-aircraft and anti-missile systems on artificial islands in the South China Sea, prompting China to defend its right to install military hardware there.

China’s exercises aim to test the equipment and troop training levels, an unidentified navy official told the official China News Service.

Last December the Defence Ministry confirmed China was building a second aircraft carrier to go with the existing vessel, but its launch date is unclear.

China keeps its aircraft carrier program a state secret, and CCTV blurred images showing the cockpit instrument panel of one aircraft involved in the Bohai Sea drills.

Beijing could build multiple aircraft carriers over the next 15 years, the Pentagon said in a report last year.

China’s successful operation of the Liaoning is the first step in what state media and some military experts believe will be the deployment of domestically built carriers by 2020.

(Reporting by Christian Shepherd and Ben Blanchard; Editing by Clarence Fernandez)