China has been incensed by U.S. military missions through the narrow strait, most frequently of warships but occasionally of aircraft, saying China "has sovereignty, sovereign rights and jurisdiction" over the waterway. Taiwan and the United States dispute that, saying it is an international waterway. The U.S. Navy's 7th fleet said the P-8A Poseidon maritime patrol and reconnaissance plane, which is also used for anti-submarine missions, flew through the strait in international airspace.

"By operating within the Taiwan Strait in accordance with international law, the United States upholds the navigational rights and freedoms of all nations," it said in a statement.

China's military described the flight as "public hype", adding it sent fighters to monitor and warn the U.S. plane.

"Troops in the theatre are always on high alert and will resolutely defend national sovereignty and security as well as regional peace and stability," the People's Liberation Army's Eastern Theatre Command said in a statement on its WeChat account.

Taiwan's defence ministry said the U.S. aircraft had stuck to the strait's median line and flew in a southerly direction on Thursday morning, and that Taiwan's forces kept watch.

The median line normally serves as an unofficial barrier between Taiwan and China.

However, since last August when China held large-scale war games around Taiwan, Chinese military aircraft have been frequently crossing the line, though generally quite briefly.

The U.S. flight followed two days of new Chinese drills near Taiwan, involving fighters, bombers and warships flying mainly to the island's south and out into the Pacific through the Bashi Channel that separates Taiwan from the Philippines.

China has not commented on the exercises, which took place less than two weeks before Taiwan stages its own annual drills and as NATO alliance leaders said China challenges its interests, security and values with its "ambitions and coercive policies".