Two US F-18 fighter jets made an emergency landing at an air force base in the southern city of Tainan yesterday, with US authorities saying one of the planes had developed a mechanical failure.
"We have launched solemn representations with the US," Hua Chunying, a foreign ministry spokeswoman, told a regular briefing in Beijing.
"We require the US to abide by the 'One-China Policy' and the three joint communiques between China and the US and to prudently deal with the relevant issue," she added, referring to agreements between the two that recognise Beijing as the sole government of China.
Several Chinese aircraft on Monday flew over the ocean for the first time via the Bashi Channel, which runs between Taiwan and the Philippines, Beijing's official Xinhua news agency said.
The US does not have formal diplomatic ties with Taiwan, officially known as the Republic of China, but has strong economic links with it and is a key military supplier.
Mark Zimmer, spokesman for the American Institute in Taiwan (AIT) -- the de facto US embassy -- said one encountered a mechanical problem and an emergency landing was requested.
The crew members and aircraft were safe, he said, adding that they had been on a "routine flight" but declining to provide details.
Taiwan's defence ministry confirmed the incident.
Beijing regularly proclaims the importance of its "One China" policy, seeing Taiwan as part of its territory awaiting reunification, and often curtails the island's involvement in international agreements.
China has been ramping up its military budget for years and expanding its capabilities and reach, raising concerns among its neighbours. Beijing says its actions are purely defensive.
