Rescue workers have dug survivors out of the rubble of a theatre in the besieged city of Mariupol which Ukraine says had been hit by a Russian air strike while people sheltered there from bombardments.
Russia denied striking the theatre.
But its forces have blasted cities and killed many civilians in its assault on Ukraine, now entering its fourth week.
Mariupol has suffered the worst humanitarian catastrophe of the war, with hundreds of thousands of civilians trapped in basements with no food, water or power as Russian forces pound it with artillery fire and air strikes.
A city mayoral adviser, Petro Andrushchenko, said the number of victims of the purported strike on the theatre on Wednesday was not known but the shelter had held.
"Now the rubble is being cleared," he told Reuters by phone.
"There are survivors."
Commercial satellite pictures showed the word "children" had been marked out on the ground in front of the building before it was hit.
Russian foreign ministry spokeswoman Maria Zakharova said the allegation that Russia had bombed the theatre was a "lie" and repeated Kremlin denials that Russian forces have targeted civilians.
"Russia's armed forces don't bomb towns and cities," she told a briefing.
Mariupol city council later said more than 350,000 people were still sheltering in the city and 30,000 had left.
The assault on Ukraine started with troops crossing the border or landing by sea and air on February 24.
But Ukraine's allies say Russian expectations of a swift victory and the removal of President Volodymyr Zelenskiy's government have been dashed and its invasion force has got bogged down.
The war has settled into a grinding pattern of sieges of cities.
The United Nations said 3.2 million civilians, mostly women and children, have now fled Ukraine to neighbouring countries.
A fourth straight day of talks between Russian and Ukrainian negotiators took place by videolink but foreign officials said the two sides remained far apart.
"Both sides are taking them (the talks) seriously but there is a very, very big gap between the positions in question," one official said.
An aide to Zelenskiy said Ukraine was sticking to its core position that it retain sovereignty over areas occupied since 2014 by Russian and pro-Russian forces.
Russian President Vladimir Putin has shown little sign of relenting, even though punitive sanctions are damaging his country's economy.
On the diplomatic front, the White House said US President Joe Biden would hold a call on Friday with Chinese leader Xi Jinping as the US tries to persuade officials in Beijing not to provide support to Russia.
Ukraine's Zelenskiy addressed the German Bundestag by video link, pulling no punches in a speech that invoked the Holocaust and the Berlin Wall, and seemed intended to shame pro-Russian politicians in Germany.
"Every year politicians repeat 'never again'," said Zelenskiy, who is of Jewish heritage, citing a remark used to mark the Holocaust.
"And now we see that these words are simply worthless. In Europe a people is being destroyed, they are trying to destroy everything that is dear to us, what we live for."
Northeastern and northwestern suburbs of Kyiv have suffered heavy damage but the capital itself has held firm, under a curfew and subjected to deadly nightly rocket attacks.
Viacheslav Chaus, governor of the region centred on the frontline northern city of Chernihiv, said 53 civilians had been killed there in the past 24 hours.
The toll could not be independently verified.
Russia has assaulted Ukraine from four directions, sending two columns towards Kyiv from the northwest and northeast, pushing in from the east near the second biggest city Kharkiv, and spreading in the south from Crimea.
Ukrainian officials have said they think Russia is running out of troops to keep fighting and could soon come to terms with its failure to topple the Ukrainian government.
Russia has said it is close to agreeing a formula that would keep Ukraine neutral, long one of its demands.
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