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.
Biden said the United States was offering an additional $800 million in security assistance to Ukraine to combat Russia's invasion, with the new package including drones and anti-aircraft systems.
Moscow has yet to capture any of Ukraine's biggest cities despite the largest assault on a European state since World War Two. More than 3 million Ukrainians have fled, and thousands have died as the war enters its fourth week.
In the capital Kyiv, at least one person died and three were wounded when a residential building was struck by a downed Russian missile emergency services said on Thursday.
Ukraine's foreign ministry said on Wednesday Russian forces dropped a powerful bomb on a theater in the besieged southern port city of Mariupol, leaving many civilians trapped and an unknown number of casualties. Reuters could not independently verify the information.
Maxar Technologies, a private U.S. company, distributed satellite imagery it said was collected on March 14 and showed the word "children" in large Russian script painted on the ground outside the red-roofed building.
The theater had been housing at least 500 civilians, according to Human Rights Watch.
"This raises serious concerns about what the intended target was in a city where civilians have already been under siege for days and telecommunications, power, water, and heating have been almost completely cut off," Belkis Wille from the rights group said.
Moscow denies targeting civilians and Russia's defense ministry said its forces had not struck the building, RIA news agency said.
Just hours after Ukrainian President Volodymyr Zelensky delivered an emotional plea to the U.S. Congress for more military aid, Biden laid out a wide range of weapons and equipment that America will provide to help Ukraine beat back the Russian invasion.
The new $800 million aid package centers on weapons that the Ukrainian military has already been using effectively against the Russians. And it includes air defense systems urgently needed to defend cities from the overwhelming barrage of missiles being launched by Russian forces.
A key element of that was Biden's vow to help Ukraine get long-range air defense systems that aren't made in America, a likely reference to the Russian-made S-300s or similar surface-to-air missile systems which other NATO nations in Eastern Europe have. Such systems are highly effective and can shoot down aircraft and intercept ballistic missiles.
A senior defense official said Wednesday that the U.S. will provide the Ukrainians with systems that they know how to use, that they're already trained and equipped to use, and that they are using with effect. Those include air defense systems that allies and partners possess and might be willing to send to Ukraine, said the official, who spoke on condition of anonymity to discuss internal talks. Defense Secretary Lloyd Austin will be in Slovakia on Thursday and is expected to discuss this issue with officials there.
Left off the list for Ukraine were two things that Zelensky has repeatedly requested, but the U.S. and NATO have firmly rejected: Russian-made MiG-29 fighter jets funneled to Ukraine via the U.S., and the establishment of a no-fly zone over Ukraine. The West believes that doing either could trigger a wider war with Russia.