US President Joe Biden has accused Russia of carrying out a "horrific atrocity", after a missile attack on a railway station in Kramatorsk in eastern Ukraine which killed at least 50 people and injuring 300.
President Biden blamed Moscow, saying its military struck civilians who were trying to evacuate and reach safety.
Russia has denied carrying out the attack.
Biden also thanked Slovakia's government for transferring a missile defense system to Ukraine, fulfilling one of Zelensky's top requests to help the country defend itself against Russia.
He said the United States will reposition a Patriot missile system to Slovakia and warned against complacency in the international effort to push back against Russia's invasion of Ukraine.