BEIJING, (Reuters) – China’s President Xi Jinping said to Joe Biden that Taiwan needs to be dealt with properly in order to prevent any negative effects on Sino-American relations.

China believes Taiwan is a separatist province that should be returned to its fold by force, if necessary. This issue has been a major focus of China’s relations with the United States.

Washington seeks Beijing’s support in restoring peace to Ukraine, following Russia’s invasion of February 24, 2014. Although Washington does not have formal diplomatic relations, Taiwan remains Taiwan’s biggest international backer as well as arms supplier.

“Some people in the United States send the wrong signals in Taiwan to pro-independence troops, and this is very dangerous,” Xi stated to Biden in a video chat.

“If Taiwan’s issue is not dealt with properly it will impact the relations between these two countries.”

China’s Shandong aircraft carrier was sailed by a U.S. destroyer through Taiwan Strait on Friday. The incident occurred just hours before U.S. Presidents Barack Obama and Donald Trump were scheduled to meet.

According to the White House, Biden stated that he reiterated with Xi in his call that the U.S. policy toward Taiwan had not changed and that Washington continues to resist unilateral changes to its status quo.

China increased its military activities near the island over the last two years to support its sovereignty claims.

“(We) hope that the U.S. side (to this issue),” Xi stated to Biden.

According to Chinese state media, Xi told Biden also that Ukraine’s war must be ended as soon as possible.

All sides should support Russia-Ukraine dialog, while NATO and the United States should hold talks with Russia in order to resolve the “crux” of Ukraine crisis.