The United Nations warns some 4 million refugees could leave Ukraine in the coming weeks. Filippo Grandi is the U.N. high commissioner for refugees.

Filippo Grandi: “As we speak, there are 520,000 refugees from Ukraine in neighboring countries. This figure has been rising exponentially, hour after hour, literally, since Thursday.”

More than half of those who’ve fled have crossed Ukraine’s western border into Poland. Foreign nationals report they’ve been barred from crossing even as Ukrainian citizens have been welcomed with open arms.