The Chinese military sent 18 planes, including fighter jets, over the Taiwan Strait in an unusually large show of force on Friday as a senior US envoy held a day of closed-door meetings on the self-governing island claimed by China.

Chinese fighter jets appeared in Taiwanese airspace from four directions, media reports from Taipei said, as Beijing launched maritime and airspace drills near the island on Friday, leading Taiwan to scramble its own warplanes. Taiwan’s defence ministry said two bombers and 16 fighter jets from China crossed into Taiwan’s air defence identification zone.

The “real combat” drills come as Keith Krach, US undersecretary of state for economic growth, energy and environment, arrived in Taiwan on Thursday, and will attend the memorial service for former Taiwan President Lee Teng-hui on Saturday. Lee, who died in July, is known on the mainland as the “godfather of Taiwan secessionism”.

“We sent the delegation to a funeral and the Chinese have apparently responded by military blustering. I’ll leave it at that,” US secretary of state Mike Pompeo told reporters during a visit to Guyana.

Krach’s visit comes within a month of US secretary of health and human services Alex Azar’s trip to Taiwan as Washington and Taipei warm up ties, much to the anger of Beijing.

In Beijing, defence ministry spokesperson Ren Guoqiang said “those who play with fire will get burnt”, as he announced the drills. He said the exercises were a “necessary move aimed at the current situation in the Taiwan Strait to safeguard national sovereignty and territorial integrity”. He accused the US and Taiwan of “stepping up collusion, frequently causing disturbances” without directly referring to Krach’s visit.

Reiterating that Taiwan is an inalienable part of China, Ren said the Taiwan question is purely China’s internal affair. Commenting on Krach’s visit, foreign ministry spokesperson Wang Wenbin said on Friday that China has the firm will to thwart external interference and secessionist acts in Taiwan.

The US official held talks with Taiwan’s minister of economic affairs and the cabinet’s vice premier. He is scheduled to meet Taiwanese President Tsai Ing-wen for dinner at her official residence.

Beijing has ramped up military activity near Taiwan in recent months and have conducted several exercises in the region.

In June, Taipei scrambled jets in response to warn off the aircraft from the People’s Liberation Army (PLA) Air Force, which had deployed fighter aircraft across the Taiwan Strait hours after a US transport plane flew over the island.

In August, Beijing conducted exercises near the island, which coincided with health secretary Azar’s visit.

The US is also preparing to sell seven tranches of weapons systems to Taiwan, the CNN reported on Thursday, quoting a US official. The US, like India and the majority of other countries, does not have formal diplomatic ties with Taiwan, though the Taiwan Relations Act of 1979 allows Washington to sell arms to the island.