U.S. House Speaker Nancy Pelosi was expected to appear in Singapore today as part of a closely watched tour of Asia that has stoked fears, including at the highest levels of the U.S. government, of dangerously heightened tensions with China over the possibility that she would make a stop in Taiwan.

Pelosi has not confirmed whether she will visit Taiwan, a self-governing democracy of 23 million people that China claims as its own territory. But she had proposed a trip to the island this year, which was postponed because she contracted the coronavirus, and when asked recently about her travels plans, she said that it was “important for us to show support for Taiwan.”

On Sunday, Pelosi revealed some more details about her itinerary, which she had previously declined to disclose, citing security concerns. Her office said in a statement that her trip, on which she would be accompanied by a small congressional delegation, would include visits to Singapore, Malaysia, South Korea and Japan to “focus on mutual security, economic partnership and democratic governance in the Indo-Pacific region.” A posting on the website of the American Chamber of Commerce in Singapore said that Pelosi would be attending a cocktail reception hosted by the group this afternoon.

The possibility of a trip to Taiwan by Pelosi — who would be the highest-ranking American official to go there since 1997, when a previous House speaker, Newt Gingrich, visited — comes at a particularly delicate time in U.S.-China relations. The Biden administration has grown increasingly worried that China’s leader, Xi Jinping, might try to move, perhaps with force, against Taiwan within the next year and a half.

Xi, China’s most authoritarian leader in decades, has pledged to pursue reunification with Taiwan, though he has not specified a timeline. Some analysts fear that he may feel pressure to show a tough stance — possibly including military action — against any perceived challenges to that pledge before an important Chinese Communist Party Congress this fall, when he is expected to claim a third term as leader.

President Joe Biden himself has seemingly alluded to the risk of a clash with China if Pelosi visits. Asked recently by reporters about the proposed trip, he said that “the military thinks it’s not a good idea right now.” The president has also been shoring up U.S. relations with Asian allies as a potential counterweight to China’s rise.

China has not specified how it would react if Pelosi’s visit went ahead. During a two-hour phone call between Xi and Biden on Thursday, their first direct conversation in four months, Xi warned Biden against “playing with fire” on the Taiwan issue, according to a Chinese government statement that did not explicitly mention the House speaker.

Others have been more direct in denouncing the potential visit. A spokesperson for China’s Foreign Ministry, Zhao Lijian, told reporters last week that China would take “firm and resolute measures” if Pelosi visited Taiwan and that the United States would be “responsible for all of the serious consequences.” Some political analysts and state media commentators have suggested that China would activate its air force to prevent the visit — raising the specter of armed conflict.

The Chinese military announced it would conduct drills Saturday with live ammunition in the waters off southeastern Fujian province, about 80 miles from Taiwan. On Sunday, a spokesperson for the Chinese air force said that the country’s fighter jets flew around Taiwan to enhance the ability to defend territorial integrity, without specifying dates.

The Biden administration insists that its stance on Taiwan has not changed, a message that Biden relayed to Xi during their phone call, according to the White House. Long-standing U.S. policy acknowledges, without endorsing, China’s position that Taiwan is part of its territory and holds that the United States would protect the island without saying exactly how.

But the president has little official authority over Pelosi and her travel plans. And rising anti-China sentiment in both the Democratic and Republican parties makes it awkward politically for Biden to openly discourage her trip.

Some Chinese and American analysts have played down the risks of military escalation, noting that Xi would probably want to avoid unpredictability before the Party Congress this year.

The Chinese government perhaps gave a foretaste of how it will respond to Pelosi’s visit when the military announced live-fire exercises in waters 80 miles from neighboring Taiwan’s coast. A spokesperson for China’s air force also declared that the force has the “firm will, full confidence and sufficient capability to defend national sovereignty and territorial integrity.”

At the same time, domestic politics, in both China and the United States, has left little room for graceful de-escalation, said Chen Qi, a professor of international relations at Tsinghua University in Beijing. It could cost the Democrats politically if Pelosi decides not to visit Taiwan, Chen said in an interview with a journalist for Xinhua, China’s state news agency. And China cannot afford to be seen as weak in the face of a perceived provocation.

“Now it’s up to who blinks first,” Chen said.