China is warning it will respond forcefully if US House Speaker Nancy Pelosi proceeds with a visit to Taiwan, the self-governing island democracy it claims as its own territory.
Ms Pelosi is second in line to the presidency and would be the highest-ranking US politician to visit Taiwan since 1997.
China has threatened unspecified "resolute and strong measures" if she proceeds with the trip, which analysts say could cause tensions to spike in the Taiwan Strait, considered a major potential Asian powder keg.
Here's a look at what's happening.
Why does Pelosi want to visit Taiwan?
Ms Pelosi has been a staunch critic of China throughout her more than three decades in Congress, once unfurling a banner on Beijing's Tiananmen Square memorialising those killed in the bloody crackdown on pro-democracy protesters in 1989.
She was also a strong supporter of 2019 pro-democracy protests in Hong Kong, making her a target of caustic criticism from Beijing.
Taiwan enjoys strong bipartisan support in Congress, and Ms Pelosi said last week it was "important for us to show support for Taiwan".
Taiwan's President Tsai Ing-wen has defied Beijing's threats and her administration has favoured core democratic values and liberal policies close to Ms Pelosi's heart, including same-sex marriage and a strong social security net.
Why would the visit cause a rise in tensions?
China claims Taiwan as its own territory, to be annexed by force if necessary, and its military build-up in recent years has largely been seen as oriented toward such a mission.
Beijing objects to all official contact between Taipei and Washington, and routinely threatens retaliation.
This time, the stakes appear to be higher.
Chinese Foreign Ministry spokesperson Zhao Lijian warned the US of "serious consequences" if Ms Pelosi's visit goes ahead.
"If the US insists on going its own way, China will certainly take firm and forceful measures to safeguard its national sovereignty and territorial integrity, and the United States should be held responsible for any serious consequences," Mr Zhao said.
China launched military exercises and fired missiles into waters near Taiwan in response to a 1995 visit to the US by Taiwan's then-president Lee Teng-hui, but its military capabilities have greatly advanced since then.
While experts say it is unlikely China would use force to prevent Ms Pelosi's US government plane from landing in Taipei, its response remains unpredictable.
Former Australian ambassador, John McCarthy AO, told the ABC Ms Pelosi's trip would disturb — to some degree — the efforts to bring about better equilibrium in the relationship between the United States and China.
"I think it would make things harder, it will erode a little bit the policy of strategic ambiguity," Mr McCarthy said.
"But I wouldn't say that that automatically leads to hostilities, withdrawal … I think things would have to go a lot further before we get to that stage."
Why is the timing sensitive?
US President Joe Biden's administration is keen to keep America's crucial but often turbulent and highly complex relationship with China on an even keel.
Ms Pelosi had planned to visit in April but postponed the trip after getting COVID-19.
She has declined to discuss reported plans to travel to Taiwan in coming weeks.
That could coincide with China's celebrations of the August 1 anniversary of the founding of the People's Liberation Army, the military wing of the ruling Communist Party, and possibly overlap with a planned phone call between Mr Biden and President Xi Jinping.
"Everything from the tensions over Taiwan, to the war in Ukraine, as well as how we better manage competition between our two nations, certainly in the economic sphere," White House national security spokesperson John Kirby said of the topics to be discussed.
"This is a call that has been scheduled for a long time and there's already a pretty robust agenda of things for these two leaders to talk about."
A more robust Chinese response could also be driven by Mr Xi's desire to bolster his nationalist credentials ahead of a party congress later this year at which he is expected to seek a third five-year term in office.
Mr Xi's expansion of his powers into every sphere, and his hardline zero-COVID response to the pandemic, have sowed a degree of resentment among some people in China.
Appealing to raw patriotism, particularly over Taiwan, might help him fend off criticism.
What is Taiwan's attitude toward a visit?
Ms Tsai has been welcoming of all foreign dignitaries, serving and retired, from the US, Europe and Asia, using such visits as a bulwark against China's refusal to deal with her government and relentless campaign of diplomatic isolation.
Still, her rhetoric on such occasions has generally been relatively low-key, reflecting her own calm demeanour and possibly a desire not to further antagonise China, which remains a crucial economic partner, with around a million Taiwanese residing in mainland China.
Senior Fellow for East Asia at the Lowy Institute, Richard McGregor, told the ABC's RN Drive program that as tensions grow between China and Taiwan, support within the self-governing island for recognition from aboard is growing.
"People naturally think that if anybody wants to make a gesture to Taiwan … that naturally everybody in Taiwan would support this. That's not always the case because they don't really want the issue to be elevated, they want maintenance of the status quo," Mr McGregor said.
"But I think things have moved on now and I think the overall mood in Taiwan is one of support for this — not from everybody — but I think the majority in Taiwan would have support because things are getting much more tense these days and they're looking for signs of support."
Taipei staged a civil defence drill on Monday, and Ms Tsai on Tuesday attended annual military exercises, although there was no direct connection with tensions over a possible visit from Ms Pelosi
While the Taiwanese public strongly rejects China's demands for unification, the ability of the island's military to defend against the PLA without US help is highly questionable, so shoring up the armed forces has been a hallmark of Ms Tsai's term in office.
Speaking on Tuesday during the exercises, Defence Ministry spokesperson Sun Li-fang said the military was monitoring all movements of Chinese warships and aircraft around the island.
"At the same time, we have the confidence and ability to ensure the security of our country," Mr Sun said.
AP/ABC — with additional reporting by Ning Pan.
