Joseph Biden said the US would defend Taiwan if China attacked, apparently departing from longstanding policy.
"Yes, we have an obligation to do that," the US president said when asked if the US would defend Taiwan.
However, a White House spokesman later told some US media outlets that Biden's statement did not mean a change in policy.
Taiwan responded, saying that Biden's statement would not change their relationship with China in any case.
China sees Taiwan as a breakaway province, which it could one day take back by force if necessary, while Taiwan claims to be a sovereign state.
The US does not have official diplomatic ties with Taiwan, but sells arms to Taiwan under the Taiwan Relations Act, which obligates America to help the island in the event of an attack.
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America has long practiced "strategic ambiguity" when it comes to the complex issue of Taiwan's defense.
This meant that the US was deliberately ambiguous about what it would do if China attacked the island.
The cabinet of the president of Taiwan reacted to Biden's statement, stating that they will not give in under Chinese pressure, but also that they will not make hasty moves when they receive the support of America.
"Taiwan will show firm determination to defend itself," presidential spokesman Xavier Cheng said.
He also confirmed that he would confirm that the Biden administration continued to show "strong" support for Taiwan.
Biden's comment came shortly after China's ambassador to the United Nations, Zhang Yun, accused the US of fueling tensions between the two countries.
"We are not the cause of the problem," he said.
"On the contrary, some countries - especially the US - are taking dangerous actions, taking the situation in the Taiwan Strait in a dangerous direction."
"I think at this point we should call on the United States to end such practices."
"Putting Taiwan into war is definitely not in anyone's interest." I don't see the United States getting anything out of it," he continued.
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When CNN's Anderson Cooper asked the second time whether the US would defend Taiwan in the event of a Chinese attack, Biden again answered in the affirmative.
A White House spokesman later tried to clarify Biden's comments to US media, saying the US was "not announcing any policy changes".
Tensions between Taiwan and China have been rising in recent weeks after Beijing sent dozens of warplanes into Taiwan's air defense zone.
Biden added that he is not worried about the conflict with China.
"There is no need to worry ... China, Russia and the rest of the world know that we are the most powerful military in the history of the world," Biden said.
"The thing to worry about is whether [China] will engage in activities that would put them in a position where they could make a serious mistake," he said.
China-Taiwan Relations - Basic Details:
- Why do China and Taiwan have bad relations? China and Taiwan split during a civil war in the 1940s, but Beijing insists the island will be returned at some point, by force if necessary.
- Who governs Taiwan? The island has a constitution, democratically elected leaders and about 300.000 active soldiers in the armed forces.
- Who recognizes Taiwan? Only a few countries recognize Taiwan. Most instead recognize the Chinese government in Beijing. The US has no official ties to Taiwan, but has a law requiring it to provide the island with defense resources
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