Sixteen people were killed in Tokmak in the southern Zaporizhzhia region after it was shelled by the Ukrainian military.
The town is held by Russia.
Yevgeny Balitsky, the region’s top official, said on Telegram that the shelling on Friday night also injured at least 20 people, 12 of them seriously.
The attack came as Ukraine’s army chief said the situation on the eastern front had worsened in recent days after the Russians intensified their armoured assaults near Bakhmut.
Russia’s defence ministry said on Saturday its forces had captured Pervomaiske, a village in the Donetsk region where Moscow has focused its offensive for months.
Meanwhile, Switzerland announced it would host a conference in June to help chart a path for peace in Ukraine after over two years of fighting.
But Vladimir Putin said a peace process couldn’t happen without Russia.
“They aren’t inviting us,” he said. “They think there’s nothing for us to do there, but at the same time they say it’s impossible to decide anything without us. It would have been funny if it weren’t so sad.”