US House Speaker Nancy Pelosi arrived in Kuala Lumpur on Tuesday, Malaysian state media reported, her second stop in an Asian tour that has sparked rage in Beijing over a possible visit to Taiwan.
China views Taiwan as its territory and has indicated through repeated warnings that it would view such a visit as a major provocation.
Pelosi landed at a Malaysian air force base ahead of meetings with the prime minister and the speaker of the lower house of parliament, state news agency Bernama reported.
After Singapore and Malaysia, her itinerary includes stops in South Korea and Japan -- but the prospect of a Taiwan trip has dominated attention.
While President Joe Biden's administration is understood to be opposed to a Taiwan stop, White House National Security Council spokesman John Kirby said Pelosi was entitled to go where she pleased.
"The speaker has the right to visit Taiwan," he told reporters.
"There is no reason for Beijing to turn a potential visit consistent with longstanding US policies into some sort of crisis."
Kirby cited intelligence that China was preparing possible military provocations that could include firing missiles in the Taiwan Strait or "large-scale" incursions into Taiwanese airspace.
He said Pelosi was travelling on a military aircraft and that while Washington did not fear a direct attack, it "raises the stakes of a miscalculation".
Taiwan's military on Tuesday said it was "determined" to defend the island against increased threats by China over the potential Pelosi visit.
Kirby reiterated, however, that US policy was unchanged toward Taiwan.
This means support for its self-ruling government, while diplomatically recognising Beijing over Taipei and opposing a formal independence declaration by Taiwan or a forceful takeover by China.
Taiwan's government has remained silent on the prospect of a Pelosi visit.
Premier Su Tseng-chang did not confirm the visit on Tuesday when asked by reporters, but thanked Pelosi for her support.
Multiple Taiwanese media outlets carried comments from deputy parliament speaker Tsai Chi-chang saying Pelosi was "very likely" to visit in the coming days.
The Liberty Times newspaper cited unnamed sources as saying she would land Tuesday night, then meet President Tsai Ing-wen the next day before departing in the afternoon.
More warnings from China
Taiwan's 23 million people have long lived with the possibility of an invasion, but the threat has intensified under Chinese President Xi Jinping.
In a call with Biden last week, Xi warned the United States against "playing with fire" on Taiwan.
And China's ambassador to the United Nations, Zhang Hun, said Monday that such a visit would be "very much dangerous, very much provocative".
If it happens, "China will take firm and strong measures to safeguard our sovereignty and territorial integrity", he said.
American officials often make discreet visits to the island to show support, but a Pelosi trip would be higher-profile than any in recent history.
"The probability of war or a serious incident is low," tweeted Bonnie Glaser, director of the Asia programme at the US-based German Marshall Fund think tank.
"But the probability that... (China) will take a series of military, economic, and diplomatic actions to show strength & resolve is not insignificant," she added.
"Likely it will seek to punish Taiwan in myriad ways."