Asked in a CBS 60 Minutes interview broadcast on Sunday whether U.S. forces would defend the democratically governed island claimed by China, he replied: "Yes, if in fact, there was an unprecedented attack."

Asked to clarify if he meant that unlike in Ukraine, U.S. forces - American men and women - would defend Taiwan in the event of a Chinese invasion, Biden replied: "Yes."

The CBS interview was just the latest time that Biden has appeared to go beyond long-standing stated U.S. policy on Taiwan, but his statement was clearer than previous ones about committing U.S. troops to the defend the island.

The United States has long stuck to a policy of "strategic ambiguity" and not making clear whether it would respond militarily to an attack on Taiwan.

Asked to comment, a White House spokesperson said U.S. policy towards Taiwan had not changed.