The US Air Force has a major base on the southern Japanese island of Okinawa, which lies close to Taiwan
Three US Air Force planes, including two B-52 bombers, flew near Taiwan on Wednesday, the island's defense ministry said, after Taiwan's air force scrambled earlier in the week to intercept Chinese jets.
The United States is Taiwan's most important international backer, even in the absence of formal diplomatic ties, and is also the island's main source of arms.
Tensions spiked between Taiwan and China, which claims the island as its own, on Sunday and Monday, as Taiwan sent F-16s to shadow approaching Chinese bombers and fighters.
China has been flying what it calls "island encirclement" drills on-off since 2016 when Taiwan President Tsai Ing-wen first took office. Beijing believes Tsai, who won re-election last month, wishes to push the island's formal independence.
Tsai says Taiwan is an independent country called the Republic of China, its official name.
Taiwan's Defence Ministry said one US MC-130, a special mission aircraft based on the C-130 Hercules transport, flew down the Taiwan Strait in a southerly direction.
The two B-52 bombers skirted Taiwan's east coast, also in a southerly direction, the ministry added.
Taiwan's armed forces monitored both sets of flights, and nothing out of the ordinary was observed, it said, without giving more details.
The US Air Force has a major base on the southern Japanese island of Okinawa, which lies close to Taiwan.
China has described its exercises on Sunday and Monday as actions to guard national sovereignty.
Taiwan has urged China to focus its efforts on fighting the new coronavirus rather than menacing the island.
Taiwan Foreign Ministry spokeswoman Joanne Ou said in a statement earlier on Wednesday that China's military activities had only caused anger on the island and harmed the peaceful development of relations across the strait.
"Our government will continue to adopt a pragmatic and restrained stance, prudently handle cross-strait relations, and deepen cooperation with countries with similar ideals, including the United States, in response to the rising Chinese military threat," she added.