China Says U.S. Trespassing in Its Airspace After Documents Sent to Taiwan

China warned of "serious consequences" for trespassing in its airspace on Thursday, hours after the U.S. Air Force delivered "diplomatic mail" to the de facto U.S. embassy in Taipei.

A C-146A Wolfhound, typically used by Air Force Special Operations Command, left Okinawa's Kadena air base in Japan before landing at Songshan airport in Taiwan's capital at 9:32 a.m. local time, according to publicly available flight tracking data.

Wu Qian, a spokesperson for China's Defense Ministry, said in an online statement that Beijing had expressed its "serious concern" over the stopover, which lasted just over half an hour.

"Taiwan is part of China's sacred and inalienable territory," Wu said. "Any foreign military aircraft that lands on Chinese territory must obtain permission from the government of the People's Republic of China."

"Any foreign ships or planes trespassing into Chinese airspace will trigger serious consequences," he added.

Taiwan's Foreign Ministry spokesperson Joanne Ou told Newsweek that the government would offer "no comments and no further explanation" about Thursday's brief visit.

According to Taiwan's TVBS News, the flight manifest showed no passengers on the plane, which had requested a stop lasting no longer than 90 minutes from local authorities. It took off 34 minutes later at 10:06 a.m.

The news report said the aircraft had delivered items intended for the handover at the American Institute in Taiwan, whose outgoing director, Brent Christensen, returned to the U.S. via Taoyuan airport on Thursday morning after a three-year posting.

His successor, Sandra Oudkirk, arrived in Taipei on Monday and is in mandatory quarantine.

It was the first time "diplomatic mail" had been delivered to Taiwan by chartered aircraft, Taipei's Apple Daily reported, presumably referring to the four decades since Washington ended formal diplomatic ties with Taipei in 1979.

The Chinese government claims the island nation as one of its provinces, despite lacking any practical jurisdiction over Taiwan.

Beijing lodged similar stern protests after a delegation of three U.S. senators visited Taipei for three hours on June 6. They had arrived in the back of a U.S. Air Force C-17 Globemaster III, with the military transport plane making headlines on both sides of the Taiwan Strait.

On April 14, China also disapproved of a less formal visit by three retired U.S. officials. The personal delegation sent by President Joe Biden affirmed Washington's continued support for Taiwan, including in its self-defense.

Thursday's statement by the Chinese Defense Ministry—issued about five hours after the cargo plane had left Taipei—warned the U.S. that it was "playing with fire."

The Taiwanese government, it added, was "leading wolves into the room"—using a Chinese idiom that can be interpreted as "inviting danger."

Update 7/15/21, 6:45 a.m. ET: This article was updated to add comments from Taiwan's Foreign Ministry.

U.S. Air Force Special Operations Airliners
File photo of C-146A Wolfhounds on the flightline at Duke Field, Florida, on October 30, 2019. A similar aircraft landed in Taipei on Thursday. Senior Airman Dylan Gentile/U.S. Air Force