US president Joe Biden has pledged to defend Taiwan militarily if China were to invade in remarks made during his first visit to Japan.

“Yes. That is the commitment we made,” Biden said at a joint news conference in Tokyo when asked whether he was willing to get involved militarily to defend Taiwan.

Speaking alongside Fumio Kishida, Japan’s prime minister, Biden added that if China were to take Taiwan by force, “it will dislocate the entire region and be another action similar to what happened in Ukraine”.

Biden’s response appeared to conflict with the decades-old US policy of “strategic ambiguity” under which Washington does not make clear if it would defend Taiwan in the face of a military attack from China.

The ambiguous stance is designed to warn Taipei not to declare independence — which would almost certainly spark a Chinese attack — while forcing the Chinese military to reconsider action against Taiwan.

Shortly after he spoke in Tokyo, the White House said US policy had not changed. “He reiterated our ‘one China policy’ and our commitment to peace and stability across the Taiwan Strait,” said a White House official. “He also reiterated our commitment under the Taiwan Relations Act to provide Taiwan with the military means to defend itself.”

The comments on Monday came as the US and Japan agreed to boost their security co-operation and deterrence capability, pointing to “China’s increasingly coercive behaviour” and the growing nuclear threat in North Korea.