TAIPEI, Taiwan (AP) — Taiwan said Tuesday it spotted 22 Chinese military aircraft and 20 vessels near the island over the previous 24 hours, as Beijing steps up its military activities in the area.

Over the weekend, the United States and Canada sailed warships through the Taiwan Strait in a challenge to China’s sweeping territorial claims. On Monday, China sailed a naval formation led by its aircraft carrier Shandong, about 70 miles (110 kilometers) to Taiwan’s southeast. The vessel was expected to conduct drills simulating aircraft, submarine, warship and land attacks, according to Chinese state media.

Thirteen of the Chinese military aircraft reported on Tuesday had crossed the median line of the Taiwan Strait, an unofficial demarcation zone between China and Taiwan, according to Taiwan’s defense ministry.

China claims Taiwan, a self-ruled democracy, as part of its territory to be reunited by force if necessary. Over the past year, Beijing has stepped up military activities around the island, including by sending warships and warplanes on a near-daily basis.

“The period from July to September this year was the peak period for the Chinese Communist Party’s exercises,” Maj. Gen. Huang Wen-Chi, the assistant deputy chief with the General Staff for Intelligence of Taiwan’s Defense Ministry, said during a press conference.

“There are a lot of warship activities in the waters surrounding the Taiwan Strait. There was also a large number of warships operating in different areas in the South China Sea and East China Sea,” he said.

Huang said the Taiwanese military would continue the monitor the movements of Chinese warplanes and warships.

On Saturday, the USS Ralph Johnson and the Royal Canadian Navy’s Halifax-class frigate HMCS Ottawa sailed through the Taiwan Strait. The timing coincided with a Group of 20 leaders’ summit in New Delhi.

The U.S. routinely sails through the strait in what it calls “freedom of navigation” operations, which China sees as provocative actions.