US President Joe Biden has given Taiwan military support in the event of an attack by China on the island.
"Yes, we are obliged to," Biden replied on Thursday at a meeting broadcast by CNN with citizens in Baltimore when asked whether the US military would defend Taiwan against China.
Military tensions between Beijing and Taipei have been increasing for years.
Beijing regards Taiwan, which split from China in 1949, as a breakaway province that should be reunited with the mainland - if necessary with military force.
China's President Xi Jinping recently repeatedly affirmed China's claim to reunification with Taiwan.
Top diplomat recommends selling arms to Taiwan
In the past few months, incidents in which Chinese fighter jets penetrated the Taiwanese air defense space increased.
In the days around the Chinese national holiday on October 1st alone, there were 150 such combat flight missions.
China and the US are at odds on many issues.
However, the Taiwan issue is considered to be the point of contention most likely to spark an armed confrontation between the world's two largest economies.
The aspiring new US ambassador to Beijing, career diplomat Nicholas Burns, said on Wednesday that China is not to be trusted on Taiwan.
In a hearing in the Senate Foreign Affairs Committee, which must confirm his nomination, Burns recommended selling more weapons to Taipei to bolster the defense.