Taiwan’s defense ministry said on Saturday it was monitoring “waves” of missile tests taking place in China’s far northern region of Inner Mongolia and that its air defense forces were on alert.

Democratically governed Taiwan, which China views as its own territory, keeps a close watch on all Chinese military activities given Beijing’s regular activities around the island, but only rarely releases details of what it sees taking place inside China.

The ministry said that from 4 a.m. (2000 GMT on Friday) it had detected “multiple waves of test launches” by China’s Rocket Force in Inner Mongolia, which lies some 2,000 km (1,200 miles) from Taiwan.

Taiwan’s forces are continuously monitoring developments and the air defense forces are on alert, the ministry said, without giving details.

China’s defense ministry did not answer calls seeking comment outside of office hours. The Rocket Force is in charge of China’s conventional and nuclear missile arsenal.

In August 2022, China fired missiles into the waters around Taiwan during war games to express anger at a visit to Taipei by then-Speaker of the U.S. House of Representatives Nancy Pelosi.

Taiwan operates powerful radar stations on some of the peaks of its central mountain range that can look far into China, according to security sources.

China detests Taiwan President Lai Ching-te, who took office in May, calling him a “separatist”, and has increased its military pressure including war games since his inauguration.