The word "children" in large letters did not stop Russian forces from destroying a theatre in Mariupol where hundreds of people were sheltering, Ukrainian authorities say.
The Russian air strike ripped apart the centre of the building, where hundreds of civilians had been living since their homes were destroyed in the fighting, Ukraine's foreign ministry said in a statement.
Many people were buried in the rubble, although there is no word on how many had been killed or injured the ministry said.
Satellite imagery from Monday showed the word "children" written in large white letters in Russian in front of and behind the Mariupol Drama Theatre.
"Another horrendous war crime in Mariupol," Ukrainian Foreign Minister Dmytro Kuleba said on Twitter, calling the bombing a "massive Russian attack".
In Moscow, the defence ministry said its forces had not struck the building and instead accused the Azov Battalion, a far-right Ukrainian militia, of blowing it up, RIA news agency said.
It did not give evidence to back up the claim.
Russia had previously accused the battalion of preventing civilians from leaving the city, which has come under heavy bombardment.
In Kyiv, residents huddled in homes and shelters amid a citywide curfew that runs until Thursday morning, as Russian troops shelled areas in and around the city, including a residential neighbourhood 2.5 kilometres from the presidential palace.
A 12-storey apartment building in central Kyiv erupted in flames after being hit by shrapnel.
In the northern city of Chernihiv, 10 people were killed while standing in line for bread, the Ukrainian General Prosecutor's Office said.
ABC/wires
