- In a post showing the Taiwanese leader giving orders on the phone, President Tsai Ing-wen condemned the incursions as an "outright provocation of regional security and stability."
- According to risk consultancy Stratfor, the incident on Sunday is "one of the most serious incursions by People's Liberation Army Air Force fighter jets on the Taiwanese side of the maritime border this century."
Taiwan's President Tsai Ing-wen has called for Chinese warplanes that cross a maritime line separating the two sides to be "forcefully expelled."
In a post showing the Taiwanese leader giving orders on the phone, Tsai condemned the incursions as an "outright provocation of regional security and stability."
"I have ordered the military to forcefully expel any incursions across the 'median line' immediately," she said, according to a CNBC translation of her post written in Chinese. The so-called median line on the Taiwan Strait separates mainland China from the island.
Taiwan scrambled aircraft to drive away the Chinese planes on Sunday, the self-ruled island's defense ministry said.
China has repeatedly sent military aircraft and ships to circle Taiwan during drills in recent years and worked to isolate the island internationally. Beijing views Taiwan as a renegade Chinese province and has sought to bring the island under its control — by force if necessary.
According to risk consultancy Stratfor, the incident on Sunday is "one of the most serious incursions by People's Liberation Army Air Force fighter jets on the Taiwanese side of the maritime border this century."
The duration of the latest incursion — about 10 minutes — implies it was intentional, and reflects escalating tensions between China and Taiwan amid the broader U.S.-China geopolitical struggle, Stratfor said in a post on Monday.
"China's apparent ending of the informal nonincursion agreement might be an effort to test Taipei's response, and it could compel Taipei to seek negotiations on avoiding escalations from such encounters," said Stratfor.
"It could result in Taiwanese fighters making their own incursions on the west side of the line, which in turn could lead to a cycle of tit-for-tat provocations coming amid already-tense cross-strait relations," the report added.
China's defense ministry did not immediately respond to CNBC's request for comments.
But during a scheduled press conference on Tuesday, China's foreign ministry spokesman Geng Shuang criticized Tsai, saying "her ridiculous words are pure nonsense and indeed infuriating." He said the latest incident "is not a diplomatic matter" and urged the U.S. to abide by Beijing's "one China" principle — which stipulates that Taiwan is a part of China.
Taiwan is one of a growing number of flashpoints in the U.S.-China relationship, which includes an ongoing trade war and Beijing's increasingly aggressive military posture in the South China Sea.
In late March, the U.S. sent Navy and Coast Guard ships through the Taiwan Strait, as part of an increase in the frequency of movement through the waterway — despite opposition from Beijing.
After the incursion on Sunday, a spokesman for Taiwan's presidential office, Huang Chung-yen, said Beijing "should stop behavior of this sort, which endangers regional peace, and not be an international troublemaker," Reuters reported.
— Reuters contributed to this report.