Taiwan is a purely internal Chinese affair that brooks no foreign interference, he added.

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"Recently the United States and Democratic Progressive Party (DPP) authorities have stepped up their collusion, frequently creating disturbances," Ren said, referring to Taiwan's ruling party.

Trying to "use Taiwan to control China" or "rely on foreigners to build oneself up" is wishful thinking and doomed to be a dead end, he added.

"Those who play with fire will get burnt," he said.

Taiwan's government did not immediately respond.

Taiwan's Liberty Times newspaper said Taiwan scrambled jets 17 times in four hours on Friday morning, warning the Chinese air force to stay away.

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It also showed a picture of missiles being loaded onto an F-16 at the Hualien air base on Taiwan's east coast.

China's announcement came as US Under-Secretary for Economic Affairs Keith Krach began the first full day of his visit to the island in a low-key way, with no open media events on his agenda.

He was due to meet President Tsai Ing-wen later and also attend a memorial service for late former president Lee Teng-hui.

China had threatened to make a "necessary response" to the trip, straining already poor ties between Beijing and both Taipei and Washington. Sino-US relations have plummeted ahead of November's US presidential election.

Chinese fighter jets briefly crossed the mid-line of the Taiwan Strait last month as the US Health Secretary Alex Azar was in Taipei.

The United States, like most countries, only has official ties with China, not Taiwan, though is the island's main arms supplier and most important international backer.

This week, the US ambassador to the United Nations had lunch with Taiwan's top envoy in New York. China's US mission said it had lodged "stern representations" over the meeting.

Reuters