update(5:10pmET): During their Sunday phone call Ukraine's President Zelensky asked Biden to visit Kiev in person amid continuing White House claims that a Russian invasion is set to happen "any day" now. 

Saying that major Ukrainian cities are "under safe protection," Zelensky suggested that a visit of the US president in person would stop the spread of panic and prevent escalation. "I am convinced that your visit to Kyiv in the coming days... would be a powerful signal and help stabilize the situation," Zelensky was quoted as saying in the call.

"We will stop any escalation. The Ukrainian capital, Kiev, other cities in our country - Kharkov and Lvov, Dnepr and Odessa - are under safe protection," Zelensky told the US president.