United States lawmakers were set to meet Taiwan's president on Monday days after China reacted to a similar visit by House Speaker Nancy Pelosi with huge military drills that raised fears of conflict.
The unannounced two-day trip came after Beijing sent warships, missiles and jets into the waters and skies around Taiwan, a self-ruled democracy that China's leaders claim and have vowed to one day seize.
The five-member congressional delegation -- led by Senator Ed Markey of Massachusetts -- was due to hold a meeting with President Tsai Ing-wen on Monday morning followed by a banquet at the foreign ministry.
Their visit will focus on trade, regional security and climate change, Washington's de facto embassy in Taipei said.
Taiwan's foreign ministry hailed the visit as another sign of a friendship between Taipei and Washington "that is not afraid of China's threats and intimidation".
But the bipartisan trip sparked another caustic response from Beijing, which has drawn down its drills but pressed on with military patrols in the Taiwan Strait.
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State news agency Xinhua published a commentary after the lawmakers' arrival Sunday with the headline 'US politicians should stop playing with fire on Taiwan question'.
It called the visiting American lawmakers opportunists thinking about their own political interests as November's midterm elections draw near.
"Those US politicians who are playing with fire on the Taiwan question should drop their wishful thinking," the agency said.
"There is no room for compromise or concessions when it comes to China's core interests," it said.
Taiwan's government has accused Beijing of using Pelosi's visit as an excuse to kickstart drills that would allow it to rehearse for an invasion.
China's communist party has never ruled Taiwan but says it will use force if necessary to take the island.
That decades-old threat was reiterated in a white paper published last week when China's Taiwan Affairs Office said it would "not renounce the use of force" against its neighbour and reserved "the option of taking all necessary measures".
It added, however: "We will only be forced to take drastic measures to respond to the provocation of separatist elements or external forces should they ever cross our red lines."
Pelosi has stood by her visit but President Joe Biden said the US military was opposed to the trip by his fellow Democrat who is second in line to the presidency after the vice president.
Congress is constitutionally an equal branch of government with lawmakers free to travel where they wish, and Taiwan enjoys bipartisan backing in divided Washington.
The United States switched diplomatic relations from Taipei to Beijing in 1979.
But it remains a key ally of Taiwan and maintains de facto diplomatic relations with Taipei.
Washington's official policy opposes both Taiwan declaring independence or China forcibly changing the island's status.
It remains deliberately ambiguous about whether it would militarily come to Taiwan's aid if China invaded.
Visits by senior US officials to Taiwan have happened for decades and even Pelosi's trip was not without precedent -- previous house speaker Newt Gingrich visited in 1997.
But the frequency and profile of US visits has increased both under former President Donald Trump and Biden.
Taiwan has also seen a flurry of delegations visit from Europe and other western allies in recent years, partly in response to Beijing's more aggressive stance under Chinese President Xi Jinping.