The attack comes as Moscow prepares to annex Ukrainian four regions into Russia after an internationally criticised vote as part of its military offensive against Ukraine.
Ukraine has blamed Russia for shelling a convoy of civilian cars in the southern Zaporizhzhia region that killed at least 25 people on the front line, drawing swift rebuttal by a pro-Kremlin official who accused Kiev's forces of carrying out the attack.
Police and emergency workers rushed to the scene of Friday's missile strike, the impact of which threw chunks of dirt into the air and sprayed the vehicles with shrapnel. The windows of the vehicles — mostly cars and three vans — were blown out.
The vehicles were packed with the occupants' belongings, blankets and suitcases. Two bodies lay in a white mini-van in front of that car, its windows blown and the sides pitted with shrapnel.
A woman who gave her name as Nataliya said she and her husband had been visiting their children in Zaporizhzhia.
"We were returning to my mother who is 90 years old. We have been spared. It’s a miracle," she said, standing with her husband beside their car.
Ukrainian President Volodymyr Zelenskyy called Russia a "terrorist state" and "bloodthirsty scum" after the strikes that also wounded 50 people.
"Only complete terrorists could do this," Zelenskyy said. "...You will definitely answer. For every lost Ukrainian life!"
Zaporizhzhia regional governor Oleksandr Starukh said Russian forces "launched a rocket attack on a civilian humanitarian convoy on the way out of the regional centre".
"People were standing in line to leave for the temporarily occupied territory, to pick up their relatives and to take away aid," he said on social media.
Governor Starukh also posted a photograph, showing two rows of crumpled cars and several corpses lying nearby.
For his part, Russia-backed official Vladimir Rogov said "the regime in Kiev is trying to portray what happened as shelling by Russian troops, resorting to a heinous provocation". He accused Ukrainian troops of carrying out a "terrorist act".
Russia, which started its military offensive against Ukraine on February 24 in what it calls a special military operation, denies deliberately targeting civilians though its attacks have devastated Ukrainian towns and cities.
The industrial hub of Zaporizhzhia, with a population of 700,000 before the conflict erupted, is under Ukrainian control but subject to Russian rocket attacks.
Part of the region is occupied by Moscow and the Kremlin has said it plans to formally annex the region at a ceremony in Moscow on Friday.
Separately, a Moscow-backed official in Kherson, a southern Ukrainian region controlled by Russia, was killed in strikes by Kiev's forces, Russia's state-run news agency cited local officials as saying on Friday.
"[Alexei] Katerinichev died as a result of a pinpoint strike from Himars. Two rockets hit the house in which he was," Kirill Stremousov, the deputy head of the Moscow-controlled region, said, referring to the US-supplied weapons systems.