Former US president Joe Biden said his successor Donald Trump's pressure on Ukraine to give up territory to Russia is a form of "modern-day appeasement" that will never satisfy Moscow.
In an interview with the BBC broadcast on Wednesday, Biden said Russian President Vladimir Putin believes Ukraine is part of "mother Russia" and "anybody who thinks he's going to stop is just foolish."
"I just don't understand how people think that if we allow a dictator, a thug, to decide he's going to take significant portions of land that aren't his, that that's going to satisfy him," he told the BBC. "I don't quite understand."