U.S. health chief Alex Azar met with Taiwan's leader on Monday (August 10) and offered the island President Donald Trump's strong support.
Azar's visit is a landmark meeting -- he's the highest-level U.S. official to go to Taiwan in four decades.
His trip angered China, which claims the democratic island as its own.
It's ratcheting up already soaring tension between the U.S. and China, and Beijing has promised unspecified retaliation.
During his visit Azar praised Taiwan President Tsai Ing-wen and her government's response to the global pandemic as among the world's best.
"Again, I am grateful to President Tsai for welcoming us to Taiwan and I look forward to using this visit to convey our admiration for Taiwan and to learn about how our shared democratic values have driven success in health."
Meanwhile, Tsai told Azar his visit represented "a huge step forward in anti-pandemic collaborations between our countries," specifically mentioning vaccine and drug research and production.
Taiwan has also expressed gratitude for U.S. support of its bid for greater access to the World Health Organization, particularly attendance at the World Health Assembly.
Taiwan is currently not a member of the WHO due to China's objections, a decision which Tsai criticized again on Monday.
"I will like to reiterate that political considerations should never take precedence over the right to health. The decision to bar Taiwan from participating in the WHA is a violation of the universal right to health."
Washington first broke off official ties with Taipei in 1979 in favour of Beijing.
But the Trump administration has made boosting arms sales and strengthening its support for the island a priority.