Photo/Illutration China’s first domestically built aircraft carrier, Shandong, launches from a dock in Dalian in April 2017. (Asahi Shimbun file photo)

BEIJING--An aircraft carrier group led by China’s newest carrier, the Shandong, has sailed through the Taiwan Strait on its way to routine drills in the South China Sea, China’s navy said on Monday, after Taiwan mobilized its forces to monitor the trip.

While it is not the first time China’s carriers have passed close to Taiwan, it comes at a time of heightened tension between Taipei and Beijing, which claims the democratically ruled island as its territory.

The Shandong carrier group sailed through the Taiwan Strait a day after a U.S. warship transited the same waterway. China’s military said it tailed the ship.

China’s navy said the Shandong and its accompanying ships had “smoothly” transited the sensitive and narrow Taiwan Strait on Sunday, heading for exercises in the South China Sea, where China has extensive and disputed territorial gains.

The drills are part of “normal arrangements made in accordance with annual plans”, it said. “In the future, we will continue to organize similar operations based on training needs.”

Taiwan’s Defense Ministry said the Shandong was accompanied by four warships and had set out from the northern Chinese port of Dalian on Thursday. Taiwan said it sent six warships and eight air force aircraft to “stand guard” and monitor the Chinese ships’ movements.

The Shandong is China’s second carrier and was formally commissioned almost exactly a year ago.

Since then, it has successfully completed tasks such as carrier-based aircraft take-off and landing and use of its weapons, the Chinese navy said.

“The combat capability of the formation system has been continuously improved in experimental training,” it added, referring to the group of warships which accompany the Shandong.

China has been working to hone its carrier operations, but has little experience compared to the United States, which has operated integrated carrier battle groups with multiple vessels for decades.