The US stands by its One China policy that sees Taiwan as a part of China, but Washington would intervene if Beijing was to use force against the island, Joe Biden said while speaking at a news conference in Tokyo on Monday.
When asked if the US would use military force, Biden replied: "Yes."
"That's the commitment we made."
A Chinese attack against the self-ruled island would "just not be appropriate," Biden said.
"It will dislocate the entire region and be another action similar to what happened in Ukraine."
He said the burden to protect Taiwan was "even stronger" after the Russian invasion of Ukraine.
China says Taiwan is 'purely internal affair'
Biden is on a five-day Asia tour. After three days in South Korea, he arrived in Tokyo Monday morning for the last leg of his trip. His statements appear to clash with the US tradition of "strategic ambiguity" as Washington usually avoids making any such explicit guarantees to Taiwan.
In response, China warned Biden not to "underestimate resolve" on the issue of Taiwan, which China considers part of its own territory.
"The Taiwan issue is a purely internal affair for China," said foreign ministry spokesman Wang Wenbin. "On issues touching on China's core interests of sovereignty and territorial integrity, China has no room for compromise or concession."
US policy towards Taiwan
The 1979 Taiwan Relations Act does not require the US to step in militarily to defend Taiwan in case of a Chinese invasion. However the policy requires the US to ensure Taiwan has the resources to defend itself and to prevent any unilateral change of status in Taiwan by Beijing.
A White House official told Reuters news agency that the US policy towards Taiwan remain unchanged.
"He [Biden] reiterated our One China Policy and our commitment to peace and stability across the Taiwan Strait. He also reiterated our commitment under the Taiwan Relations Act to provide Taiwan with the military means to defend itself," the official said.
Under the "One China" policy, the US recognizes Beijing's influence, and does not have official diplomatic ties with Taiwan. However, it does maintain unofficial contact with Taiwan, and has a de facto embassy in capital Taipei.
The US also supplies military equipment to Taiwan.
