An attack on a maternity hospital in the city of Mariupol has killed three people including a six-year-old girl, Ukrainian authorities have said.
Deputy mayor Sergei Orlov said 17 others had been injured in the attack, including pregnant women.
He told the BBC: "I'm absolutely sure they know about this facility and this is their third hospital that they are destroying in this city.
"I'm absolutely sure (these are their) targets."
Pregnant women are being pulled from the rubble of the bombed hospital amid a desperate search for survivors in sub-zero temperatures.
The children's and maternity hospital was targeted by Russian forces on Wednesday afternoon, leaving a child among three people dead, Ukrainian authorities said.
Rescuers worked through the night to free anyone still trapped under the carnage, as temperatures drop to below -4C, sparking fears for those who have been pinned under the wreckage.
Many of the pregnant women had been sheltering in the basement of the hospital as the city has come under heavy strikes since Vladimir Putin began their invasion 15 days ago.
Footage of the aftermath of the attack was posted online, showing badly damaged hospital buildings, wards with windows blown out and ceilings caved in.
Snow fell as families poured into the destroyed car park, looking around them at the carnage left behind by the attack.
Russia has denied an attack at the maternity hospital took place, branding the reports as "fake news" because the building was a former maternity hospital that had long been taken over by troops.
"That’s how fake news is born," Dmitry Polyanskiy, Russia's first deputy permanent representative to the United Nations, said on Twitter.
Polyanskiy said Russia had warned on 7 March that the hospital had been turned into a military object from which Ukrainians were firing.
Ukrainian President Volodymyr Zelenskyy said the Russian target on the maternity hospital was the "ultimate proof that what is happening is the genocide of Ukrainians".
In a statement released from the Presidential Palace in Kyiv, Zelenskyy said: "Europeans, you can't say you didn't see what is happening. You have to tighten the sanctions until Russia can't continue their savage war.
"What kind of country bombs hospitals? Is afraid of hospitals? Of a maternity ward?
"Was someone insulting Russians? Were pregnant women shooting in direction of Rostov? Was it the ''denazification'' of a hospital? What the Russians did at Mariupol was beyond savagery."
Mariupol has been under siege from Russian forces for over a week, with its residents cut off from food, water, electricity and vital medicines.
Mass graves have been dug as people die from thirst, as Mariupol mayor Vadim Boychenko said a six-year-old girl called Tanya had died "alone, exhausted, frightened, terribly thirsty."
There have been attempts to evacuate residents from the besieged city, but Russian troops have been accused of targeted the very routes they said would be safe.
Ukrainian Deputy Prime Minister Iryna Vereshchuk said an attempted evacuation from Mariupol failed on Tuesday because Russian troops fired on a convoy carrying humanitarian cargo.
And on Thursday another attempt failed after Russian shelling prevented a humanitarian convoy reaching the besieged Ukrainian city, local officials said.
Petro Andrushenko, an adviser to the mayor of Mariupol, told Reuters that Russian aircraft were targeting the routes that humanitarian aid was trying to use to enter the city, and along which buses were being prepared to evacuate people.
"We try and try and try, but I'm not sure if it'll be possible today - or other days," he said by phone.
"Airstrikes started from the early morning. Airstrike after airstrike. All the historic centre is under bombardment."
The bombardment, he said, had continued "without any gaps, without any pause", hitting houses and buildings along the evacuation routes.
"They want to absolutely delete our city, delete our people. They want to stop any evacuation," he said.
Watch: Mariupol hospital heavily damaged after suspected Russian attack
Boris Johnson condemned the attack as "depraved", and said the UK was considering more support for Ukraine to defend itself against airstrikes and would hold Putin to account “for his terrible crimes”.
In Washington, Foreign Secretary Liz Truss said the strike was “absolutely abhorrent”, but continued to reject calls from the government in Kyiv for a no-fly zone.
“The reality is that setting up a no-fly zone would lead to a direct confrontation between Nato and Russia, and that is not what we’re looking at,” she told a joint news conference with US Secretary of State Antony Blinken.
“What we’re looking at is making sure that the Ukrainians are able to defend their open country with the best possible selection of anti-tank weapons and anti-air defence systems.”