A United Nations' report says the civilian death toll in Ukraine has exceeded 7,000 since the Russian invasion began last February.
At least 40 people were confirmed to have been killed in Saturday's missile strike on a 9-story apartment building in the eastern city of Dnipro.
Ukraine's emergency authorities said on Monday that three children were among the victims, and that 25 others remain unaccounted for.
Russia claimed that the building in Dnipro was struck as a result of Ukrainian air defense actions.
Ukraine's President Volodymyr Zelenskyy condemned Moscow. In a video address on Monday, he said, "Every person guilty of this war crime will be identified and brought to justice."
UN Secretary-General Antonio Guterres also strongly criticized the missile strike. In a statement released through a spokesperson, Guterres said, "Attacks against civilians and civilian infrastructure violate international humanitarian law." He added that, "they must end immediately."
The Office of the UN High Commissioner for Human Rights reported on Monday that at least 7,031 civilians were killed in Ukraine between February 24 last year, when the invasion began, and January 15. It said 433 of the victims were children.