Trump said Taiwan "never even came up as a subject" when he met the Chinese president in South Korea on Thursday for their first face-to-face meeting in six years.

Asked on CBS's "60 Minutes" whether he would order US forces into action if China moved militarily on Taiwan, Trump said: "You'll find out if it happens, and he understands the answer to that."

But Trump declined to spell out what he meant in the interview conducted Friday at his Mar-a-Lago resort in Florida, adding: "I can't give away my secrets. The other side knows."

The US president claimed that Xi and those close to him had "openly said" that "'we would never do anything while President Trump is president,' because they know the consequences."

China claims self-governing Taiwan as its territory. Under longstanding policy, the United States recognizes only Beijing but provides weapons for the island's self-defense.

The issue continues to provoke tensions, which Trump and Xi appeared to have avoided at their summit, focusing instead on easing the trade war between Washington and Beijing.