A nine-year-old girl, her mother and another woman were killed during a Russian missile strike on Kyiv after the air raid shelter they rushed to failed to open, witnesses said.
It was the highest casualty toll from a single Russian attack on Kyiv over the past month.
"The entrance was closed, there were already maybe five to 10 women with children," local resident Yaroslav Ryabchuk said.
"They knocked loudly enough … They tried to enter the shelter, no one opened up for them. My wife died."
Mayor Vitali Klitschko said authorities were investigating why the shelter – which was at a medical facility — was locked, preventing some people from taking shelter during the bombardment.
"Were there people in it? Because, according to rescuers, after the damage to the polyclinic, a group of people were taken out of it," Mr Klitschko wrote on the Telegram messaging app.
He gave orders to the heads of the city's districts to immediately check if all the shelters in Kyiv are accessible.
Attacks strike on Children's Day
The latest Russian attack, using what Ukrainian officials said were short-range Iskander ground-launched missiles, coincided with events scheduled in Kyiv to celebrate International Children's Day.
Those events were cancelled.
Ukrainian air defences shot down all 10 cruise and ballistic missiles launched by the Kremlin's forces, but falling debris caused damage and casualties on the ground, wounding 16 people, according to authorities.
Russia has kept up a steady barrage on the Ukrainian capital and other parts of the country in recent weeks as Kyiv readies what it says is a counteroffensive to push back Moscow's troops, 15 months after their full-scale invasion.
Kyiv was the target of a reported 17 drone and missile attacks last month.
Ukraine's first lady Olena Zelenskyy said one child was in hospital after the attack.
"Children's Day has to be about safe childhood, summer, life," she tweeted.
"But today it is about new crimes of [Russia] against children."
More than 500 children killed in conflict
UN human rights monitors said six children were killed and 34 were wounded in Ukraine in the last month alone.
Since February 2022, at least 525 children have been killed and at least 1,047 have been injured, according to the UN's Human Rights Monitoring Mission in Ukraine.
"Sadly, as the world marks International Children's Day, there is little to celebrate in Ukraine where civilians, including children, continue to pay a heavy price," Matilda Bogner, the mission's chief, said.
The Ukrainian Ministry of Defence cited different figures for child casualties in the war, saying at least 484 children have been killed and 992 injured.
It was not immediately possible to reconcile the differences with the UN figures.
Russia has repeatedly targeted Kyiv with waves of drone and missile attacks since the start of the invasion, but attacks against the capital have significantly intensified over the past month.
Thursday's onslaught – the 18th this month – also damaged apartment buildings, a medical clinic, a water pipeline and cars.
Across Ukraine, the presidential office on Thursday said a total of seven civilians were killed and 27 injured over the previous 24 hours.
NATO discusses speeding up Ukraine accession
Moscow cannot stop Ukraine from becoming a NATO member, the alliance's chief Jens Stoltenberg said on Thursday, as divisions among allies about the speed of Kyiv's accession became apparent only weeks before a decisive mid-July summit in Vilnius.
"All allies agree that Moscow does not have a veto against NATO enlargement," Mr Stoltenberg told reporters as NATO foreign ministers gathered in Oslo, seeking to dispel any signs of discord ahead of the summit.
"We are moving; allies agree that Ukraine will become a member."
Ukrainian President Volodymyr Zelenskyy, speaking at a meeting of more than 40 European leaders in Moldova, said Kyiv wanted to receive a "clear" decision on its future in NATO at the summit.
NATO agreed in 2008 that Ukraine would eventually join the alliance but leaders have so far stopped short of taking steps, such as giving Kyiv a membership action plan, that would lay out a timetable for bringing Ukraine closer to the military pact.
At the Vilnius summit, NATO leaders aim to send a strong message of support to Kyiv. But with only six weeks to go, pressure is building for allies to find common ground on what exactly to offer Ukraine.
While Kyiv and its closest allies in eastern Europe call for concrete steps to bring Ukraine closer to membership, Western governments such as the United States and Germany are wary of any move that might take the alliance closer to war with Russia.
At the meeting, Mr Stoltenberg also called for a framework of security guarantees for Kyiv designed to deter Russia from again taking military action against the country.
But details will still need to be worked out, he said.
Russia blames Kyiv for new border attacks
Russia said the border region of Belgorod has again come under artillery fire from Ukraine.
Russia's defence ministry said it had repelled three cross-border attacks on Thursday (local time) near the town of Shebekino, and it accused Ukraine of using what it said were "terrorist formations" to carry out attempted attacks on Russian civilians.
"The selfless actions of Russian servicemen repelled three attacks by Ukrainian terrorist formations," the Russian ministry said.
"No violations of the state border were allowed."
More than 50 Ukrainian fighters were killed and four armoured vehicles were destroyed, the ministry said.
It added that up to 70 fighters, five tanks and four armoured vehicles were involved in the attack.
Governor Vyacheslav Gladkov said Ukraine's armed forces had shelled Shebekino with Soviet-designed Grad 122 mm rockets, setting alight a dormitory and damaging an administrative building.
At least nine civilians were injured in shelling across the region, he said.
Ukraine denies its military is involved in the incursions into Belgorod and says they are conducted by Russian volunteer fighters.
Moscow blames Ukrainian "terrorists" for targeting Russia's western border. Russian officials say the group of fighters is a proxy run by Ukraine.
Groups claim to plan cross-border raids
Earlier, a group that calls itself the Russian Volunteer Corps and purports to include Russians fighting on the Ukrainian side released a video claiming that its forces were on the border with Russia and about to launch a cross-border raid on Shebekino
A similar group that calls itself the Freedom of Russia Legion also announced a plan to launch a cross-border raid.
Belgorod Governor Vyacheslav Gladkov said that Ukrainian shelling left eight people wounded overnight, but said there had been no incursion by enemy forces.
Some Russian media outlets said that Ukrainian forces made an attempt to cross the border but were repelled by Russian troops.
The two groups also claimed responsibility for a cross-border raid last month, one of the most serious such attacks on Russian territory which prompted authorities to evacuate residents of a town near the border.
Some observers saw the raids as part of Ukrainian efforts to probe Russian defences and distract Moscow's military resources ahead of a planned Ukrainian counteroffensive.
Wires/ABC
