President Volodymyr Zelenskiy vowed to punish those responsible for the warehouse explosion late on Friday, which caused one of the highest death tolls in months and appeared to be the second such occurrence in two months.
Dozens were injured and more than 370 people evacuated from the area of the strike in the village of Myla, Zelenskiy said.
Nearby infrastructure suffered "significant damage", he added, including residential buildings and a facility providing care for the elderly.
"Those who allowed this to happen must be held accountable for their decisions," Zelenskiy wrote on X.
"There are regulations in place – ammunition cannot be stored near homes or other residential areas. Appropriate conclusions will certainly be drawn."
Russia has escalated its air war on Ukraine, using more ballistic missiles and jet-powered drones that are difficult to shoot down.
Nine other regions had been targeted in overnight strikes by Russia, Zelenskiy added, saying Kyiv in particular was under "virtually non-stop attack" from high-speed drones.
On Saturday, sirens blared throughout the morning for a third straight day as Ukraine's air force warned of new waves of drones approaching the capital.
The sound of air defences could be heard booming across the sky.
Kyiv region governor Tymur Tkachenko said a 14-year-old girl was killed in a morning drone strike on the Boryspil district. In Kyiv, a 2-year-old girl was killed by a downed drone, Mayor Vitali Klitschko said on Saturday.
Strikes in and around Kyiv on Thursday and Friday had damaged warehouses and homes, part of what some Ukrainian officials said was a campaign aimed at "paralysing" the city of several million.
Friday's blast follows a similar incident in the Kyiv-area town of Vyshneve last month, when 10 people were killed and hundreds of houses damaged after a strike triggered secondary explosions.
"In the fifth year of full-scale war, we have no right to allow a repetition of tragedies like the one that occurred in Vyshneve, and this one in the Bucha district," Prime Minister Sergiy Koretskyi, who visited the site of Friday's blast, posted on Telegram.
Zelenskiy said criminal cases had already been opened on charges of official negligence. Ukrainian officials rarely disclose damage to military targets from Russian attacks.
