This week, Taiwan's defense ministry said the island's military has sent forces to monitor a Chinese naval formation, led by the aircraft carrier Shandong, that entered the Taiwan Strait.
The formation sailed into the narrow Taiwan Strait on November 8 afternoon in a northerly direction, but it kept to the Chinese side of the waterway's median line, an unofficial barrier between the two, the ministry added.
The Taiwan Strait is not an international waterway and it alone has sovereignty there, Beijing stressed.
Taiwan and the U.S. dispute this claim, and the latter frequently sends warships through the strait.
On November 6, Japan's defense ministry said that the Shandong and other naval ships had sailed to the South China Sea after conducting landing drills in the Pacific Ocean for nine days.
The Shandong also sailed through the Taiwan Strait in June.
On several occasions, Taipei has complained about Chinese air force planes crossing the strait's median line.
China, which has never renounced the use of force to bring Taiwan under its control, has increased military activity near the democratically governed island, responding to what it claimed was "collusion" between Taiwan and the U.S.
Taipei rejects Beijing's claim of sovereignty.