WASHINGTON - China's incursions across the median line that is the tacitly accepted unofficial border with Taiwan have been very specific to what Beijing sees as provocation from the US, says The Straits Times global affairs correspondent Goh Sui Noi.

In August, when US Health Secretary Alex Azar visited Taiwan - the highest level US visitor since 1979 - it could be argued that the visit was related to Taiwan's much-admired response to the coronavirus pandemic.

But when Undersecretary of State Keith Krach arrived in Taiwan on Sept 18 to represent the United States at a memorial service for former Taiwan president Lee Teng-hui, it was seen as clearly political in Beijing.

China on Sept 18 and 19 sent warplanes across the median line, triggering Taiwanese F-16s to scramble in response.

In a way, it is a tit for tat, said Ms Goh.

The message is "You cross my line on the One China policy, I'm going to cross yours, on the median line", Ms Goh told ST Asian Insider, the weekly online video and podcast hosted by The Straits Times US bureau chief Nirmal Ghosh.

"The Chinese are using that median line to warn, to pressure both Taiwan and the US to not push the envelope on Taiwan independence," she said.

While there is a sharper sense of unpredictability of the situation in the Taiwan Strait, China has since then sent only one plane, which was a military transport aircraft, to Taiwan's Air Defence Identification Zone. It did not, however, cross the median line.

China is being careful as well, Ms Goh said.

Given its all other challenges and priorities, it cannot afford a hot war in the Taiwan Strait at this time, said Ms Goh, who has reported from both China and Taiwan for The Straits Times.