Two Chinese air force fighter jets briefly crossed the midway line over the Taiwan Strait into the unofficial airspace of the island nation on Monday, drawing the attention of surface-to-air missile defense systems, Taiwan’s defense ministry said.

The incursion was only the third time since 2016 Chinese military aircraft had strayed over the midpoint between China and Taiwan, the Hindustan Times reported.

It came on the same day as the visit of U.S. Health and Human Secretary Alex Azar’s visit to Taiwan, the highest level American to officially visit the country since the United States broke diplomatic ties in 1979.

Taiwan’s defense ministry said the J-10 and J-11 Chinese aircraft had been “strongly driven…out.”

“The Air Force Command expresses that the deliberate intrusion and move that damages the Taiwan Strait situation has seriously hurt regional safety and stability,” it said in a statement, according to the Hong Kong-based South China Morning Post. “It should be stressed that Taiwan’s military has fully grasped all developments near the Taiwan Strait and airspace, and can respond appropriately to any changes in the enemy’s situation to ensure national security.”

The incident is the latest aggressive military action by the mainland Chinese, which considers Taiwan a renegade province. Last month Chinese military aircraft encroached upon Taiwan’s self-declared air defense identification zone five times in 10 days before being chased off by Taiwanese fighter aircraft, Reuters reported.

Azar is in Taiwan particularly to improve cooperation with the island nation in combating the outbreak of the novel coronavirus as well as other health issues.

Beijing has protested Azar's visit as a betrayal of U.S. commitments to avoid official contact with the island, CBS reported.

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