Ukraine's interior minister and a child were among at least 14 people killed when a helicopter crashed into a kindergarten and set it ablaze in a suburb of the capital Kyiv.
At least 25 people were injured, including 11 children.
The crash came four days after a Russian missile struck an apartment building in the city of Dnipro, killing dozens of civilians, including six children — the deadliest attack on civilians in months.
Here's what we know so far.
Who was on board and why?
Ukrainian authorities say there were five interior ministry officials, one national police official and three crew members on board the helicopter.
All nine died in the crash.
They include Interior Minister Denys Monastyrskyi, 42, who oversaw the country's police and emergency services.
He is the most senior official to have died since Russia invaded nearly 11 months ago.
Also on board were his first deputy minister Yevhen Yenin and state secretary Yurii Lubkovych.
A national police official and Tetiana Shutiak, an aide to Mr Monastyrskyi in the internal affairs ministry, also died in the crash.
The Ukrainian Ambassador to Australia Vasyl Myroshnychenko, said he knew Mr Yenin and Mr Lukkovych personally.
"It was extremely saddening and I was shocked to hear about that," he said, speaking with ABC News Radio's Thomas Oriti.
The officials on the helicopter were due to visit Ukraine's north-eastern Kharkiv region, local police chief Volodymyr Tymoshko said, adding on Facebook that they were "not just leaders," but "friends who I respected".
Michael Bociurkiw, a global affairs analyst and senior fellow at the Atlantic Council who is based in Odesa, told the ABC the interior ministry officials were on a work trip, and were often leaving and returning from base after visiting hot spots.
What was the damage on the ground?
A child and three others on the ground were killed after the helicopter, a French-manufactured Super Puma, slammed into a building in Bovary, a north-eastern suburb of the capital Kyiv.
The crash site was reported to be on the grounds of a kindergarten in the centre of a residential courtyard.
The crash set off a large fire, and an entire side of the local kindergarten building was charred.
Several bodies lay on the ground of a courtyard, their boots sticking out from under blankets.
Residents described seeing wounded people and children, hearing screams, and seeing debris "strewn all around".
Parents recounted the terror of the immediate aftermath of the crash, and described how they and teachers evacuated children.
The helicopter wreckage later lay crumpled by an apartment block, rotor blades resting against the entrance.
Above the charred entrance to the two-storey kindergarten building was a gaping hole several feet wide.
People left flowers and soft toys at a small makeshift memorial at the site.
Emergency services were still identifying remains and the death toll could rise.
What caused the accident?
President Volodymyr Zelenskyy called it a "terrible tragedy" and said he had asked the country's SBU intelligence service to launch a criminal investigation.
"This is not an accident because it has been due to war and the war has many dimensions, not just on the battlefields," he said during a speech at the World Economic Forum in Davos.
"There are no accidents at wartime. These are all war results."
Ukrainian officials have not suggested the crash was an attack by Russian forces waging war in Ukraine.
Air force spokesperson Yuriy Ihnat said it could take several weeks to investigate the disaster.
Mr Bociurkiw said on such trips helicopters tended to fly very fast and very low to avoid enemy missile fire.
Routinely travelling at low altitudes and high speeds can increase the inherent dangers associated with the flights.
It was also reported to be a foggy day.
ABC's John Lyons, on the scene, told AM the instant reaction from some Ukrainians was that Russia must be involved somehow and they were still reeling after attack on Dnipro apartment.
"But my own enquiries here have suggested strongly, that the investigation is showing that in fact Russia was not involved in this, that it was an accident," he said.
The tragedy may prompt Kyiv to institute a rule many countries and companies follow: that more than one top official shouldn't fly on the same aircraft, political analyst Volodymyr Fesenko said.
Earlier, Ukrainian MP Inna Sovsun said investigators were looking at a number of possible causes and weren't ruling out foul play.
"They're looking at three potential explanations. One of them is the pilot's mistake, second one is technical failure and the third one is intervention in the function of the helicopter," she said.
"So we're not discarding the possibility that this was intentional but we just don't know."
"We don't know what happened, an investigation is ongoing," Mr Myroshnychenko said.
What are the implications for Ukraine?
The death of the interior minister, along with the rest of his ministry's leadership and the entire helicopter crew, was the latest devastating development for the country already ravaged by war.
He was in charge of police and emergency services that dealt with the consequences of Russian strikes and de-mining, political analyst Mr Fesenko said.
Prime Minister Denys Shmyhal said National Police Chief Ihor Klymenko had been appointed acting interior minister.
Mr Bociurkiw said Mr Monastyrskyi, who had served as interior minister since July 2021, had a key cabinet position and had been with Mr Zelenskyy since the start of his campaign.
His appointment was seen as a shake up to a ministry plagued by prior allegations of corruption.
"[He] represented a new, fresh face of the government, and that even adds to the loss," he said.
The ambassador said the deceased minister was widely respected.
"He was regarded as one of the best ministers of internal affairs we've ever had," Mr Myroshnychenko said.
He said the incident came at a critical time in the war.
"This is probably the worst time in Ukraine for that to happen, at a time when Russia is waging a war and police and minister of internal affairs is very important and very significant in our fight against Russia."
ABC/wires
