WASHINGTON — The Biden administration is increasingly concerned that a planned trip by House Speaker Nancy Pelosi to Taiwan next month could spark a major crisis across the Taiwan Strait, and the White House and an array of national security officials have briefed Pelosi and her team about the risks of traveling now, administration officials said.

If Pelosi, D-Calif., follows through with the trip, she would be the first House speaker to visit the self-ruled island in 25 years. China claims Taiwan as its own, while the United States has bolstered economic ties and arms sales to the democratically governed island. Taiwan is the single most contentious and volatile issue in the U.S.-China relationship, which has fallen to its worst state in years.

Chinese leaders would see Pelosi’s trip as a purposeful provocation by the United States, administration officials fear. Defense, military and intelligence officials have “tried to explain the risks associated with the timing of her proposed trip,” said one administration official, speaking on condition of anonymity because of the matter’s sensitivity. “But everyone understands that this is her decision.” Among those briefing Pelosi were Gen. Mark Milley, chairman of the Joint Chiefs of Staff, officials said.

President Joe Biden himself on Wednesday told reporters that “the military thinks it’s not a good idea right now” that Pelosi travels to Taiwan. Distrust between Washington and Beijing is at a heightened level, as China has acted with increased aggressiveness in recent encounters with the United States and allied military forces in the region.

The timing is also sensitive as the trip would take place only a few months before a major Communist Party Conference, when Beijing is likely to respond more aggressively to perceived provocations. In particular, President Xi Jinping, who is expected to achieve an unprecedented third term as leader, is keen not to suffer any slights in the lead-up to the conference.

Pelosi responded to Biden by saying that she is not advocating for Taiwanese independence, which is a red line for China. “I think that it’s important for us to show support for Taiwan,” she said at her weekly news conference Thursday, adding, “None of us has ever said we’re for independence when it comes to Taiwan. That’s up to Taiwan to decide.”

Such a rift between the nation’s two most powerful Democrats, who have worked closely on issues from health care to the Ukraine war, is highly unusual. About one-third of Pelosi’s congressional district is Asian American and taking on China has long been a major part of her political identity, making her a figure particularly reviled by Beijing.

Some China hawks have seized on the tension, arguing that if Pelosi refrains from visiting Taiwan it will amount to giving Beijing a veto over U.S. foreign policy. “This pathetic self-deterrence is a mistake, and it will invite more aggression,” said Sen. Tom Cotton, R-Ark.

But the administration official said it’s not a question of caving to China. “This is not an issue of standing with Taiwan,” the official said. “The issue really is that there is substantial concern across the region that this will be seen by many as provocative, and will cause China to respond in potentially unpredictable ways.”

The official also stressed that the administration cannot tell Pelosi what to do. “There’s no question but that people understand clearly [that] now, of all times, we have to respect separation of powers,” the official said.

The controversy initially erupted after the Financial Times on Tuesday reported that Pelosi, as part of a broader tour of Asia, was planning a trip to Taiwan, prompting Beijing to react with fury and urge Washington to halt the trip. “If the U.S. insists on going its own way, China will take firm and forceful measures to firmly safeguard national sovereignty and territorial integrity,” spokesman Zhao Lijian told reporters in Beijing. “The U.S. must bear all the consequence of the visit.”

Administration officials said Beijing is unlikely to make a distinction between Pelosi and Biden, or to understand that the president cannot order her not to go. The Chinese would simply view the trip as a provocation by the U.S. government, they said.

China pledges to achieve what it calls “reunification” with Taiwan, threatening to use force if necessary to take control of the island democracy. The United States has for decades walked a fine line, siding neither with Beijing’s claim to sovereignty over Taiwan nor with Taipei’s assertion of sovereignty and stating repeatedly that it opposes any unilateral changes to the status quo. Washington says it does not support Taiwanese independence.

Pelosi’s office has not confirmed the trip, and Pelosi said she never discusses her travel plans, citing security issues. But as House speaker, she likely would fly on a military plane to the island, which could be especially irritating to the Chinese.

For now, administration officials are walking delicately - hoping to dissuade Pelosi without causing a public dust-up - but concerns about the potential fallout from her trip are widespread within the executive branch.

“There’s a majority view across the administration that this would not be a great time for Pelosi to visit Taiwan,” said Bonnie Glaser, director of the German Marshall Fund’s Asia Program. “China has been signaling in all sorts of ways that it would respond strongly to her visit.’‘

She added, “We are at an increasingly dangerous point in the U.S.-China relationship, particularly on Taiwan, with both sides determined to demonstrate resolve in the region.”

The war in Ukraine has raised the stakes even higher. Many Asian leaders have voiced fears that Russia’s effort to take over Ukraine could embolden China to move aggressively into Taiwan, which is similarly a self-governing entity coveted by a neighboring superpower.

Beijing’s military has made repeated incursions into Taiwan’s air defense identification zone, declared this year that the Taiwan Strait is not international waters, and had an increasing number of encounters with the U.S. military in the South China Sea. The latter led Milley to order a review of hundreds of U.S. military interactions with Chinese forces over the last five years.

The Biden administration has had “substantial engagement with Taiwan” over the past several months, the official noted, further raising Beijing’s anxieties. “The Chinese have substantial worries that we are taking steps to change the status quo,” the official said. “They have sent very clear signals with respect to [Pelosi’s trip], and they have made some specific public warnings.”

In April, Pelosi planned a visit to Taiwan that was canceled when she tested positive for the coronavirus. But reports at the time of the impending visit drew swift rebukes from senior Chinese officials.

“If the U.S. House speaker, a political leader of the United States, deliberately visits Taiwan, it would be a malicious provocation against China’s sovereignty and gross interference in China’s internal affairs, and would send an extremely dangerous political signal to the outside world,” said Chinese Foreign Minister Wang Yi in a call with a French official in April.

A string of actions and remarks by Biden and former U.S. officials have shifted Beijing’s perceptions of U.S. strategic intentions, analysts said.

In March, former secretary of state Mike Pompeo traveled to the island and urged the United States to formally recognize Taiwan. And this week, former defense secretary Mark Esper in Taipei said that Washington’s one-China policy had “outlived its usefulness.” Hours later, a U.S. warship passed through the Taiwan Strait.

In May, Biden said the United States would intervene militarily if China were to invade Taiwan - an usually explicit promise to protect the island - although the White House said the comment did not reflect a shift in U.S. official policy.

Beyond that, the United States has for decades sold arms to Taiwan, which lies 100 miles across the Taiwan Strait from mainland China, and has pushed for Taiwan to be involved in international bodies such as the World Health Organization.

Pelosi’s planned trip “shows the U.S. side continues to underestimate China’s resolve on the Taiwan question,” said a Chinese official, speaking on condition of anonymity as is typical in the country. “The U.S. side is wrong to believe that it can continue to flagrantly disregard the feelings of the Chinese side on Taiwan without more serious consequences.”

The official added: “In the past, Nancy Pelosi has openly threatened China’s development, and we are very aware of her position on Chinese affairs. This was very clear in her actions and words on Hong Kong . . . actors like Nancy Pelosi are committed to destabilizing China under the guise of morality.”

Pelosi has in recent years become a lightning rod for criticism by Chinese officials and state media over her criticism of China’s human rights record in Hong Kong, a territory that was long administered by Great Britain but transferred to Chinese control in 1997. Beijing’s Foreign Ministry in 2021 cited meetings between Pelosi and high-profile pro-democracy protestors, many of whom have since been jailed. It said she “openly urged rioters to take illegal and violent actions against the central government.”

More recently, China’s foreign ministry accused Pelosi of “playing despicable political games” after she urged global leaders not to attend the 2022 Winter Olympics in Beijing, citing the county’s human rights record.

Beijing does not buy the administration’s assertion that it has no authority to order Pelosi not to travel. “The U.S. side has the ability to stop these clowns from performing in Taiwan,” the Beijing official said. “Over and over, it chooses not to.”

The last major cross-strait crisis was in 1995-1996, and before that there were two in the 1950s. “We’re at risk of sleepwalking into a fourth Taiwan Strait crisis,” said Zack Cooper, a senior fellow with the American Enterprise Institute. “I understand Pelosi’s logic,” he added, but “I’d been hearing from the Chinese that there’s a view that maybe a crisis is necessary to demonstrate China’s seriousness on Taiwan.”

Some in the administration fear that China might challenge Pelosi’s aircraft, or ‘‘escort” it by flying a Chinese military jet over Taiwan, which would be an unprecedented step.

The administration has made strides in bringing European and east Asian nations together in recognizing the importance of “peace and stability in the Taiwan Strait.” South Korea in particular, in a departure from its typically vague position, adopted the Taiwan language for the first time in a joint statement with the United States last year. Now the administration is concerned that Beijing could spin a Pelosi trip as a pretext to undermine that stability, making it harder to preserve the group’s support.

More broadly, the controversy reflects the increasing significance of Taiwan in U.S.-China relations, said Evan Medeiros, a former top White House China expert in the Obama administration.

“The Taiwan issue is no longer a boutique regional issue,” said Medeiros, who was part of an unofficial U.S. delegation that visited Taipei in March in a show of support. “It now is a global issue and may emerge as the central arena of the U.S.-China competition. It could spark war - including nuclear war - between the two largest economies in the world.”

The Washington Post’s Dan Lamothe and John Hudson contributed to this report.