Addressing the UN Security Council via videolink, Ukraine President Volodymyr Zelensky accused Russia of "crimes against humanity" after a new missile barrage caused blackouts across Ukraine.
He stated that the Russian "formula of terror" had forced "millions of people to stay without energy supplies, without heating, without water" in sub-zero cold.
The strikes killed at least seven people, Ukraine said. Nuclear power plants went off-line.
Zelensky addressed an urgent UN Security Council meeting on Russian attacks that have caused blackouts in neighboring Moldova, diplomats said.
Earlier, the Ukrainian leader said in a tweet that he had instructed his country's ambassador to the world body, Sergiy Kyslytsya, to ask for the meeting.
"Murder of civilians, ruining of civilian infrastructure are acts of terror. Ukraine keeps demanding a resolute response of international community to these crimes," Zelensky said.
In a letter to the Council's president requesting the meeting, seen by AFP, Kyslytsya wrote that Russia "has committed another act of terror against the civilian population of Ukraine" with Wednesday's strikes.
The air assault battered Ukraine's already failing electricity grid, leaving several dead and disconnecting three nuclear power stations from the grid.
The Ukrainian military said Russian forces had fired around 70 cruise missiles at targets across the country yesterday and also deployed attack drones.