seoul, South Korea - A U.S. congressional delegation led by House Speaker Nancy Pelosi is expected to arrive late Tuesday in Taiwan, defying warnings by China, which has threatened a military response to the visit.

Pelosi will arrive around 10:30 p.m. local time, according to Taiwanese media reports. She is expected to meet Wednesday with Taiwanese President Tsai Ing-wen and other senior lawmakers.

For weeks, media have speculated whether Pelosi, a prominent China critic, would go ahead with the Taiwan stop.

China has warned the visit would be an unacceptable violation of what it sees as its sovereignty over the self-ruled island.

Zhao Lijian, Chinese foreign ministry spokesman, on Monday warned the country's military will not 'sit idly by" but will take "strong countermeasures to uphold China's sovereignty and territorial integrity."

Planes, ships on the move

Early Tuesday, several Chinese warplanes and warships neared the median line in the Taiwan Strait, according to an unnamed source quoted by the Reuters news agency.

The source said the Chinese aircraft conducted "very provocative" tactical moves of briefly "touching" the unofficial dividing line and circling back to the other side of the strait. Taiwan dispatched aircraft to monitor the situation, Reuters added.

White House officials on Monday refused to confirm Pelosi's visit but urged China to refrain from any military provocations.

"There is no reason for Beijing to turn a potential visit consistent with long-standing U.S. policy into some sort of crisis conflict or use it as a pretext to increase aggressive military activity in or around the Taiwan Strait," said John Kirby, a White House National Security Council official.

Kirby expressed concern China could respond by firing missiles around Taiwan, conducting large-scale military exercises, or sending a large number of planes across the median line. China could also pursue "spurious legal claims," such as asserting that the Taiwan Strait is not an international waterway, he said.

Split after civil war

Taiwan and China split in 1949 after a civil war, with the defeated nationalist forces fleeing to Taiwan and setting up a government that later grew into a vibrant democracy.

Since then, China's Communist Party has vowed to take Taiwan, using force if necessary, even though the island has never been ruled by the Communist Party.

The United States formally cut official relations with Taiwan in 1979 when it switched diplomatic recognition to China. However, the United States continued to maintain unofficial relations with Taiwan and supplies it with defensive weapons as mandated by the U.S. Congress.

For decades, that balancing act helped preserve cross-strait peace, but in recent years Chinese leaders have grown concerned Washington may be shifting toward more explicit support for Taiwan.

On three occasions, United States President Joe Biden has indicated the U.S. would defend Taiwan militarily if China invaded.

Though U.S. officials deny there has been any change in policy, Biden's comments differed from that of many of his predecessors, who employed a tactic of "strategic ambiguity" when it comes to Taiwan's defense.

In this context, Pelosi's visit appears even more concerning to China, according to Amanda Hsiao, a senior Taiwan-based analyst at the International Crisis Group.

"We've seen very clear messages coming out of Beijing that China intends on responding forcefully if the visit goes through. And I think those signals should be taken quite seriously," Hsiao told VOA.

Hsiao expects a "significant increase" in Chinese military activities around Taiwan during and after Pelosi's visit. China has already flown a record high number of warplanes around Taiwan's Air Defense Identification Zone in recent months.

It would be the highest-level U.S. visit to Taiwan since 1997, when former House Speaker Newt Gingrich led a congressional delegation there.

In an interview with VOA's Mandarin Service, Gingrich expressed support for Pelosi's trip, which he said will likely only amount to "an irritation" to U.S.-China ties. "I think this is at one level a lot of noise about nothing," Gingrich said.

But many analysts warn that China has grown much more powerful and bold since the late 1990s, when Gingrich visited.

"I think the China we're dealing with now, under [President] Xi Jinping, is more assertive, more ambitious, and more concerned, I think, with appearing weak in these sorts of moments," Hsiao said.

Another factor: an upcoming Communist Party Congress, where Xi is expected to secure a controversial third term as China's top leader. It's unclear, though, how the meeting will affect China's response.

"They would still prefer to have a relatively stable external environment while they're undergoing this key transition," Hsiao said. "But on the other hand, because it is on the eve of the 20th Party Congress, the leadership is under some pressure to demonstrate that it won't be taken advantage of."

In Taiwan, a large portion of residents are relieved that Pelosi appears to be moving ahead with the visit, which they believe shows U.S. commitment to preserving peace in the Taiwan Strait, according to William Yang, a Taipei-based journalist and president of the Taiwan Foreign Correspondents' Club.

"But I think on the other hand, there is a group of Taiwanese people who are very suspicious about the intention and the purpose and the effect of the visits,' he said. 'A lot of them are questioning whether this is actually going to accelerate the pace of angering China, pushing China to take a more unwise and unreasonable action against Taiwan - especially with the Russian invasion of Ukraine."