International outrage over Russia's invasion of Ukraine grew on Thursday as U.S. and Ukrainian officials said civilians waiting in line for bread and sheltering in a theater had been killed by Russian forces.

U.S. President Joe Biden called Russian leader Vladimir Putin a war criminal in comments the Kremlin said were "unforgivable" as it insisted the war in Ukraine was "going to plan" amid talk of compromise at peace talks.

Moscow has yet to capture any of Ukraine's biggest cities despite the largest assault on a European state since World War II. More than 3 million Ukrainians have fled and thousands have died as the war enters its fourth week.