TAIPEI (Taiwan News) — Chinese Foreign Minister Wang Yi warned US Secretary of State Marco Rubio that Taiwan is the “biggest point of risk” in bilateral ties, as both sides prepare for a possible leaders summit this month, Reuters reported Thursday.

In a phone call on Thursday, Yi said Taiwan is one of China’s “core interests” and urged Washington to “keep its promises” to maintain stability in relations. He called on the US to make the “right choices” to open space for cooperation and contribute to global peace.

The exchange comes ahead of an expected meeting in Beijing between US President Donald Trump and Chinese leader Xi Jinping on May 14-15, per The Guardian.

Wang said China and the US should prepare for important high-level exchanges and work to expand cooperation while managing differences. He added that bilateral ties have “generally remained stable” under the leadership of Xi and Trump.

The two sides also discussed the situation in the Middle East, according to a Chinese government summary, though no details were provided. The call marked their first publicly disclosed conversation since late February.

Wang and Rubio last met in person in Munich in February, at a time when trade tensions between the world’s two largest economies had eased. A fragile tariff truce was reached during a Trump-Xi meeting in South Korea in October.