Shelling has killed at least 28 people at a bakery in the Russian-occupied city of Lysychansk, Moscow-installed officials have said.
At least one child is among the dead, local leader Leonid Pasechnik wrote in a statement on Telegram.
He said a further 10 people were rescued from under the rubble by emergency services.
He blamed Ukraine for the shelling, but officials in Kyiv did not comment on the incident.
Both Moscow and Kyiv have increasingly relied on longer-range attacks this winter amid largely unchanged positions on the 930-mile front line in the nearly two-year-old war.
However, Ukrainian forces have come under intense Russian attack over the past 24 hours, with continuous assaults along the front line, Ukraine’s general staff said in a statement on Sunday.
Fighting has been particularly fierce in the eastern city of Avdiivka, where Moscow is attempting to encircle Kyiv’s troops, while Ukrainian forces have also been on the defensive in Kupiansk, Lyman, Bakhmut and Zaporizhzhia, officials said.
The military administration for Ukraine’s Sumy region said on Sunday that Russian forces had shelled the region in 16 separate attacks the previous day, firing on the border communities of Yunakivka, Bilopillia, Krasnopillia, Velyka Pysarivka, and Esman.