President Donald Trump touted relations with China as "extremely strong" on Monday following a call with Chinese leader Xi Jinping, who told Trump that Taiwan's "return to China" is a key part of Beijing's vision for the world order, Reuters reported.

The call, not previously flagged by either country, came weeks after the two leaders met in South Korea, where they agreed to a framework for a trade deal that has yet to be finalized.

China is locked in its biggest diplomatic crisis for years with U.S. ally Japan. This month, Japanese Prime Minister Sanae Takaichi said any Chinese attack on democratically governed Taiwan could trigger a Japanese military response, according to Reuters.