China began combat drills near the Taiwan Strait on Friday, the same day a senior US official began high-level meetings in Taipei, as tensions rose and Beijing denounced tightening ties between Chinese-claimed Taiwan and the United States.
Beijing has watched with growing alarm the ever-closer relationship between Taipei and Washington, and has stepped up military exercises near the island, including two days of mass air and sea drills last week.
Chinese Defence Ministry spokesman Ren Guoqiang said Friday's drills, about which he gave no details, were taking place near the Taiwan Strait and involved the People's Liberation Army's eastern theatre command.
"They are a reasonable, necessary action aimed at the current situation in the Taiwan Strait and protecting national sovereignty and territorial integrity," Ren said.
Taiwan is a purely internal Chinese affair that brooks no foreign interference, he added.
"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 air force jets scrambled 17 times on Friday morning over four hours, warning China's air force to stay away.
It also showed a picture of missiles being loaded onto an F-16 at the Hualien air base on Taiwan's east coast.
Hu Xijin, editor of China's widely read state-backed Global Times tabloid, wrote on his Weibo microblog that the drills were preparation for an attack on Taiwan should the need arise, and that they were valuable experience, enabling gathering of intelligence about Taiwan's defensive systems.
"If the US secretary of state or defence secretary visits Taiwan, People's Liberation Army fighters should fly over Taiwan island, and directly exercise in the skies above it," he added.
China's announcement came as US Undersecretary for Economic Affairs Keith Krach began the first full day of his visit to Taiwan in a low-key way, with no open media events on his agenda.
He is due to meet President Tsai Ing-wen later in the day, and on Saturday will attend a memorial service for late 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, and last week China carried out two days of large-scale drills off Taiwan's southwestern coast.
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 UN mission said it had lodged "stern representations" over the meeting.