Chinese President Xi Jinping told U.S. President Donald Trump that Taiwan’s “return to China” is a key element of the post-World War II international order, according to state media.

Xi emphasized that the U.S. and China once fought together in WWII and should now cooperate to preserve its outcomes.

The call came amid China’s heightened tensions with Japan following comments suggesting Tokyo could respond militarily to a Chinese attack on Taiwan.

Xi said U.S.–China relations have improved since his October meeting with Trump, noting resumed soybean purchases and reduced U.S. tariffs, Reuters has reported.

The two leaders also discussed the war in Ukraine, with Xi reiterating China’s support for efforts aimed at achieving peace.