A delegation of five US senators and a congressman arrived in Taiwan on Thursday for a two-day visit that was quickly denounced by China, which claims the island as its territory.
The politicians, led by Republican Senator Lindsey Graham, were due to meet the island's president, Tsai Ing-wen, and the defence minister.
Taiwan's Foreign Ministry said the visit highlighted America's "rock solid" support to Taiwan amid a “severe” situation in Ukraine.
In Beijing, Chinese Foreign Ministry spokesman Zhao Lijian denounced the visit, saying “China is firmly opposed to any form of official exchanges between the US and Taiwan".
China has held military exercises near the island in recent months.
Chinese President Xi Jinping said last year that he wanted a peaceful "reunification" with Taiwan.
Washington is Taiwan's most important international backer and arms supplier, a frequent source of friction in Sino-US relations.
“Relevant US lawmakers should abide by the one-China policy upheld by the US government," Mr Zhao said.
"The US should … stop official contacts with Taiwan, and avoid going further down the dangerous path.
“We will continue to take strong measures to resolutely safeguard national sovereignty and territorial integrity."
Mr Graham was joined by Senator Robert Menendez, chairman of the influential Senate foreign relations committee, Senator Richard Burr, Senator Robert Portman, Senator Benjamin Sasse and Congressman Ronny Jackson.
The visit follows an announcement last week that US House of Representatives Speaker Nancy Pelosi would visit Taiwan.
But Ms Pelosi’s trip was postponed after she tested positive for Covid-19.