At least six people died early Thursday as Russia launched a wave of missiles into Ukraine.
It was the first large missile attack by Russia since the middle of February.
The attack cut off electricity in several places including Kyiv and Kharkiv. The strikes also made Europe's largest nuclear plant switch to its emergency cooling system to avoid dangerous overheating. Nuclear power centers need to be connected to electricity to operate such cooling systems.
The Zaporizhzhia nuclear center is now reconnected, but many thousands of people are still without heat or electricity.
Every time there is an attack near the power plant, said Rafael Grossi of the International Atomic Energy Agency, "we are rolling a dice." Grossi said "one day our luck will run out" and there will be an accident.
The attacks targeted areas in western Ukraine, far from the main battle lines.
The Russian Defense Ministry said the strikes were Russia's answer to a Ukrainian attack in the Bryansk part of western Russia.
Ukraine said the attack in Russia did not happen, and Russia was making a false claim to justify the missile attack.
Ukrainian officials said Russia launched 81 missiles and eight drones on Thursday. The Ukrainian military stopped 34 missiles and four drones, but it said the different kinds of weapons made the defense difficult.
Included in the attack were six hypersonic, or very high-speed missiles. Experts say they are Russia's most modern missiles and Ukraine's military cannot stop them.
The attack continues Russia's earlier efforts to strike Ukraine's power system. Experts have said Russia thinks knocking out heat and electricity will make Ukrainian leaders more willing to give land to Russia in return for a peace deal.
Oleh Zhdanov is a Ukrainian military expert. He told the Associated Press that Thursday's attack did not hurt the Ukrainian army but damaged "the nerves of the civilian population of Ukraine."
Many in Kyiv and Kharkiv, Ukraine's two largest cities, were without heat on a day when the temperature was about zero degrees Celsius.
Ukrainian President Volodymyr Zelenskyy released a statement about the attack.
"The occupiers can only terrorize civilians," he said. "That's all they can do. But it won't help them. They won't avoid responsibility for everything they have done."
Dmytro Kuleba is Ukraine's Foreign Minister. On Twitter he wrote: "No military objective, just Russian barbarism."
The Reuters news agency reported that at least five people were killed in an area close to the western city of Lviv.
Oksana Ostapenko lives in the western village of Zolochiv where she was standing outside of her sister's destroyed home. She said her sister and two others have not been found. She thinks they did not escape.
"They still haven't found them. We were hoping that they're alive. But they're not alive," she said.
In Kyiv, 57-year-old Viktor Bukhta said a missile landed in his neighborhood and people were injured. He said he was burned trying to put out a fire.
Ukrainian officials said six people were killed in other attacks Wednesday and Thursday.
I'm Dan Friedell.