U.S. House Speaker Nancy Pelosi is expected to visit Taiwan on Tuesday, defying Chinese authorities who have warned of consequences if the trip takes place, according to people familiar with her plans.

It would be a landmark move by a U.S. official that raises the risk of a military confrontation, given China views Taiwan as its territory. Pelosi would become the highest-ranking American politician to visit the island in 25 years, since then-House Speaker Newt Gingrich in 1997.

One of the people said a meeting with President Tsai Ing-wen is on Pelosi's schedule for Wednesday, although another person said such a meeting is still in flux.

Pelosi's planned visit was reported earlier by the Liberty Times, one of Taiwan's pro-ruling party newspapers.

Her visit will likely elicit an angry response from China, which promised "grave consequences" for diplomatic relations. President Xi Jinping told President Joe Biden on a call last week he would "resolutely safeguard China's national sovereignty and territorial integrity" and that "whoever plays with fire will get burnt."

Under the 1978 agreement to normalize relations between China and the U.S., Washington agreed to recognize only Beijing as the government of China, and Taiwan as part of China. But the U.S. has insisted that any reunification between the island and mainland must be peaceful, and has supplied Taiwan with advanced weaponry while remaining deliberately ambiguous about whether U.S. forces would help defend against a Chinese attack.

Pelosi, who represents a San Francisco district where almost a third of residents are of Asian ancestry, has long positioned herself as a China hawk. She opposed China's ascension to the World Trade Organization and on a trip to Beijing in 1991, famously unfurled a banner in Tiananmen Square honoring protesters killed in a crackdown by the ruling Communist Party two years earlier.

China's reaction to Pelosi's visit will be closely watched. A spokesman for the White House National Security Council, John Kirby, said on MSNBC Monday that Beijing shouldn't view her trip as a provocation.

"If anything, you would think the Chinese would welcome it because it shows consistency. It shows that nothing has changed about America's One China Policy adherence," Kirby said. "It shows that nothing has changed about our obligations under the Taiwan Relations Act to help with Taiwan's self-defense."

He added that it's "disconcerting that the Chinese might use this as some sort of pretext to actually increase the tensions."

Chinese Foreign Ministry spokesman Zhao Lijian made clear at a Monday news briefing, however, that Pelosi's stature as the No. 3 official in the U.S. made her trip highly sensitive, reiterating the army "won't sit idly by."

Chinese media outlets including the Communist Party's Global Times have suggested the People's Liberation Army would respond aggressively to a Pelosi trip, possibly by sending warplanes right over the island.

Taiwan would then need to decide whether to shoot them down, a move that could trigger a wider military conflict. China would have to weigh the possibility that America and its allies in the region would be drawn in militarily.

Biden said in May that Washington would intervene to defend Taiwan in any attack from China, although the White House later clarified he meant the U.S. would provide weapons, in accordance with existing agreements.

Despite the risk of conflict, U.S. lawmakers from both parties have expressed support for Pelosi's trip, arguing it's important that the top leader in Congress doesn't cave to pressure from Beijing.

"If we can allow the Chinese to dictate who can visit Taiwan and who cannot, then we have already ceded Taiwan to the Chinese," said Senate Foreign Relations Chair Bob Menendez, a New Jersey Democrat, who made his own trip to Taiwan in April.

Visits by lower-level U.S. lawmakers have also prompted military responses by China. Last November, Chinese warplanes flew around the east side of the island after a visit by a U.S. congressional delegation.

The last major crisis in Taiwan came in 1995-96, when China lobbed missiles into the sea near ports and then-President Bill Clinton sent two aircraft carrier battle groups to the area. Gingrich visited both Taiwan and China the year after that episode, telling Beijing the U.S. would defend the island.