Taiwan’s Defence Ministry said Saturday it was monitoring “waves of test-firing” by China’s missile unit in a region more than 1,600 kilometres (1,000 miles) from the self-ruled island and that its air force stepped up its alertness.

China views the democratic island as a breakaway province that should be reunified with the mainland.

According to Taiwan’s military news agency, the ministry had detected “multiple waves of test-firing operations” by China’s Rocket Force in Inner Mongolia on Saturday. It did not give details on the tests taken by the force, which takes charge of China’s arsenal of missiles.

It is not immediately clear whether the tests were related to China’s harassment of Taiwan. In recent years, China has ramped up its military activities around the island, which is ruled by the Democratic Progressive Party.

In May, Taiwan’s newly elected President Lai Ching-te said in his inauguration speech that he wants peace with China and urged it to stop its military threats and intimidation of the island.

China’s military has displayed a strong show of force toward Taiwan since Wednesday, when the US new top envoy to Taipei promised that Washington would help the island defend itself.

Taiwan’s Defence Ministry said Thursday it had detected 66 warplanes around the island and that dozens flew across the median line in the Taiwan Strait, the de facto boundary between the two sides.

On Saturday, 30 warplanes also were detected around Taiwan over a 24-hour period with 20 crossing the median line.

The US, like most countries, does not recognise Taiwan. But it’s the island’s main partner and is bound by US laws to provide it with the means to defend itself. Less than a month ago, the US State Department approved the sale to Taiwan of missiles and drones for an estimated $360 million.