Ukraine has opened an investigation after it was reported a number of its soldiers were killed by a Russian missile strike during an "award ceremony" this week, officials said.
The Ukrainska Pravda media outlet said over 20 Ukrainian soldiers from an assault brigade died in the attack, which took place in the southern region of Zaporizhzhia on Friday.
AFP was not able to immediately verify the circumstances of the strike.
Defense Minister Rustem Umerov called the incident a "tragedy" and ordered a full investigation.
"We must make every effort to protect our people and give honest answers to the families and friends of the fallen soldiers," he said Saturday evening.
The Ukrainian army confirmed a number of soldiers had been killed, but did not say how many.
"On November 3, the enemy conducted insidious attacks in the direction of Zaporizhzhia," it said Saturday.
"In particular, it fired an Iskander-M missile at the personnel of the 128th Mountain Assault Brigade, killing the soldiers and causing injuries of varying severity to local residents," the army added.
One Ukrainian soldier said on social media that 22 people from the brigade had been killed and that they were gathered for an award ceremony.
"Everyone is writing that 'Heroes died'. Although it is more appropriate to write 'Heroes became victims'," soldier Ivan Savytskyy said.
"They became victims of military rudimentary traditionalism in its worst form," he said.
Ukraine's western Zakarpattia region, where the assault brigade is based, will observe a three-day mourning period starting Monday, local governor Victor Mykyta said.
"Our heroes are alive as long as the memory of them and their deeds lives on," he said Sunday.