US House of Representatives Speaker Nancy Pelosi will spend Tuesday night in Taiwan, three sources say, as the US says it will not be intimidated by Chinese threats to never “sit idly by” if she makes the trip to the self-ruled island claimed by Beijing.

Ms Pelosi, who began an Asia trip on Monday in Singapore, was due to spend Tuesday night in Taiwan, three people briefed on the matter said.

Taiwan’s foreign ministry said it had no comment on reports of Ms Pelosi’s travel plans but the White House, which would not confirm the trip, said she had the right to go.

China’s responses could include firing missiles near Taiwan, large-scale air or naval activities, or further “spurious legal claims” such as Beijing’s assertion that the Taiwan Strait was not an international waterway, White House national security spokesman John Kirby told reporters in Washington.

“We will not take the bait or engage in sabre rattling. At the same time, we will not be intimidated,” Mr Kirby said.

Amid widespread speculation over whether she would make a stop in Taiwan, Ms Pelosi’s office said on Sunday that she was leading a congressional delegation to the region that would include visits to Singapore, Malaysia, South Korea and Japan. It did not mention Taiwan.

One source told Reuters the US had informed some allies about Ms Pelosi’s visit to Taiwan.

Two other sources said Ms Pelosi was scheduled to meet a small group of activists who are outspoken about China’s human rights record during her stay in Taiwan.

Chinese foreign ministry spokesman Zhao Lijian said on Monday that it would be “a gross interference in China’s internal affairs” if Ms Pelosi visited Taiwan, and warned it would lead to “very serious developments and consequences”.

“We would like to tell the United States once again that China is standing by, the Chinese People’s Liberation Army will never sit idly by, and China will take resolute responses and strong countermeasures to defend its sovereignty and territorial integrity,” Mr Zhao told a daily briefing.

China views visits by US officials to Taiwan as sending an encouraging signal to the pro-independence camp in the island. Washington does not have official diplomatic ties with Taiwan but is bound by US law to provide the island with the means to defend itself.

A visit by Ms Pelosi, a longtime critic of China, would come amid worsening ties between Washington and Beijing.

Mr Kirby said nothing about Ms Pelosi’s possible trip changed US policy towards Taiwan, and Beijing was well aware the division in powers within the US government meant Ms Pelosi would make her own decisions about the visit.

During a phone call last Thursday, Chinese President Xi Jinping warned US President Joe Biden that Washington should abide by the one-China principle and “those who play with fire will perish by it”.

Mr Biden told Xi that US policy on Taiwan had not changed and that Washington strongly opposed unilateral efforts to change the status quo or undermine peace and stability across the Taiwan Strait.

On Monday, Taiwan Premier Su Tseng-chang did not directly respond when asked whether Ms Pelosi would visit but said that visits by “distinguished foreign guests” were welcome.

On Monday, Ms Pelosi and her delegation met Singapore Prime Minister Lee Hsien Loong, and discussed issues including cross-strait relations, the Ukraine war and climate change, Singapore’s foreign ministry said.

Beijing considers Taiwan to be part of its territory and has never renounced using force to bring the island under its control. Taiwan rejects China’s sovereignty claims and says only its people can decide the island’s future.

Mr Biden said last week he thought the US military believed a visit by Ms Pelosi to Taiwan was “not a good idea right now”.