A U.S. navy destroyer has been following the Chinese aircraft carrier the Liaoning since Sunday, as Beijing’s military aircraft continue incursions into Taiwan’s air defense identification zone (ADIZ).

The U.S. Arleigh Burke-class destroyer navigated the Philippine Sea and crossed paths with the Chinese carrier battle group, before trailing the Liaoning, a Type 054A-class missile frigate, a 052D destroyer, a 055 destroyer and a 901 replenishment oiler, it was reported by Taiwanese media on Tuesday.

The news service was citing @OSINT_1, a Twitter account analyzing images from Earth imaging company Planet Labs.

The Liaoning earlier this month was seen conducting naval exercises near Taiwan, where the government is on alert after a low-altitude flight of a Chinese spy plane in Taiwan’s ADIZ.

The People’s Liberation Army’s Y-9 tactical reconnaissance plane entered Taiwan’s zone on Monday morning, flying at a low altitude of 30 meters or 100 feet, the South China Morning Post reported, citing SouthwestAirspaceofTW, a Facebook page tracking activities near Taiwan.

The Facebook page also stated Taiwan’s military scrambled aircraft and issued radio warnings.

Taiwanese analyst Lin Yin-yu at the Institute of Strategic and International Affairs at National Chung Cheng University in southern Taiwan, said the flight was testing Taiwanese radar capabilities.

“Usually, radar signals will be obstructed by certain topography such as a mountain. By flying at an altitude of 30 meters, the PLA plane was testing if it could fly beneath the radio wave coverage area,” Lin said, according to the Post.

Chinese aircraft have entered Taiwan’s ADIZ more than 200 times this year, according to Taipei.

China also delivered to its military three new warships, a Type 075 landing helicopter dock, Type 055 destroyer and Type 094 submarine during a ceremony on Hainan Island on Friday.

Taiwan’s director of intelligence Cheng Ming-tung said Monday Taipei has information about the new warships in Hainan. Chen also raised concerns about tensions in the South China Sea, according to Taiwan media.

Beijing and Taipei are in disagreement over China’s one-China policy, which does not recognize the sovereign status of Taiwan.