Hong Kong CNN  — 

Taiwan’s President has accused Beijing of purposefully inflaming tensions in East Asia, after Chinese warplanes crossed the sensitive median line across the narrow strait that separates the mainland and the self-governing island almost 40 times on Friday and Saturday.

Taken together, the repeated incursions, which came from multiple directions and involved a combination of sophisticated fighter jets and heavy bombers, is without modern precedent and marks a significant escalation in cross-strait tensions.

“What we are seeing now is not just a situation across the Taiwan Strait, but a regional situation. China’s recent military activities, especially in the past few days, clearly constitute a threat of force, which is part of their verbal attacks and military threats (against Taiwan),” President Tsai Ing-wen told reporters Sunday.

The uptick in Chinese military activity came as Keith Krach, the United States under secretary of state for economic, energy and environmental affairs, held meetings in the island’s capital Taipei, ahead of a memorial service on Saturday for former Taiwan President Lee Teng-hui.

The three-day visit to the island was denounced by Beijing, with a spokesman for the country’s Foreign Ministry demanding the two sides “immediately stop” official exchanges.

China has reacted with increasing anger at warming ties between Taipei and Washington, and has ramped up military drills in the waters around the island which Beijing continues to view as an inseparable part of its territory despite the two sides have been governed separately for over seven decades.

Taiwan Defense Ministry photo shows an Chinese People's Liberation Army Air Force H-6 bomber intercepted by Taiwanese fighters on Friday.

The Taiwan Strait median line has been an informal but largely respected border of control for Beijing and Taipei. According to Taiwan and United States government reports, prior to the weekend, Beijing’s warplanes had only crossed it intentionally three times since 1999 – once in March 2019, once in February of this year, and again during a visit by US Health and Human Services Secretary Alex Azar in August this year.

On Friday and Saturday, a total of 37 Chinese aircraft, a mixture of H-6 bombers, J-10, J-11 and J-16 fighters, and an Y-8 antisubmarine warfare plane crossed the median line, according to Taiwan’s Defense Ministry press releases.

The ministry said in a statement that it “issued radio warnings, scrambled fighters and deployed air defense missile systems to monitor the activities.” In her remarks, Tsai said that such actions would make other countries in the region “more aware of the threat posed by China.”

On Monday, Beijing said its forces are operating legally. “Taiwan is an inalienable part of Chinese territory, and there is no so-called median line,” Foreign Ministry spokesperson Wang Wenbin said.

Keith Krach, a US undersecretary of state, attends a funeral ceremony of former Taiwan President Lee Teng-hui in Taipei on September 19, 2020.

‘A threat of force’

The US has maintained close ties with Taiwan since the island split from mainland China in 1949 after the end of a bloody civil war. But since Washington and Beijing established formal diplomatic ties in 1979, the US had largely refrained from sending high-level officials to Taipei so as to not antagonize the Chinese government.

China’s leader, President Xi Jinping, has been clear in his ambitions to “reunify” the island with the mainland, and has refused to rule out the use of force, even though the ruling Chinese Communist Party has never exerted direct control over Taiwan.

The Eastern Theater Command of the Chinese People’s Liberation Army (PLA) said in a statement on Friday said that the recent exercises were made necessary owing to the “current situation across the Taiwan Strait.”

A spokesman added that Chinese troops had the “confidence and determination to thwart any attempt by any person or force to carry out ‘Taiwan independence’ separatist activities in any form.”

A detailed