US President Joe Biden on Saturday called his Russian counterpart Vladimir Putin a "butcher" while meeting Ukrainian refugees at the National Stadium in Warsaw.
Asked by reporters what he thought of Putin's actions, Biden responded simply: "He's a butcher".
Biden said he had been asked by children to pray for their male relatives fighting in Ukraine.
"I remember what it's like when you have someone in a war zone and every morning you get up and you wonder, you are just wondering, you are praying you don't get that phone call," said Biden, whose son Beau served in Iraq before dying of a brain tumour.
On Friday, the US president spoke to US soldiers stationed in Poland near the Ukrainian border and aid workers helping refugees fleeing the conflict.
He praised Ukrainians for showing "backbone" against the Russian invasion and compared their resistance to the Tiananmen Square pro-democracy protests in China in 1989.
