Russian missile strikes have crippled almost half of Ukraine's energy system, the government said on Friday, and authorities in the capital Kyiv warned that the city could face a "complete shutdown" of the power grid as winter sets in.
With temperatures falling and Kyiv seeing its first snow, officials were working to restore power nationwide after some of the heaviest bombardment of Ukrainian civilian infrastructure in nine months of war.
The United Nations has warned of a humanitarian disaster in Ukraine this winter due to power and water shortages.
"Unfortunately Russia continues to carry out missile strikes on Ukraine's civilian and critical infrastructure. Almost half of our energy system is disabled," Prime Minister Denys Shmyhal said on Friday.
He was speaking at a joint news conference with a vice-president of the European Commission, Valdis Dombrovskis, who offered Ukraine the 27-nation bloc's "unwavering support".
Engineers have been racing to repair the power grid in Kyiv.
"We are preparing for different scenarios, including a complete shutdown," Mykola Povoroznyk, deputy head of the Kyiv city administration, said in televised comments.
President Volodymyr Zelenskiy said earlier about 10 million people were without power in a country with a pre-war population of about 44 million. He said authorities in some areas ordered forced emergency blackouts.
Ukraine's national grid operator Ukrenergo said Russia had launched six large-scale missile attacks on Ukraine's energy infrastructure from October 10 to November 15.
Russia's defence ministry said its forces had used long-range weapons on Thursday to strike defence and industrial facilities, including "missile manufacturing facilities".
Russian forces swept into Ukraine on February 24 in what Moscow said was a special military operation to eliminate dangerous nationalists. Kyiv calls Russia's action an unprovoked imperialist land grab.
Russian forces plundered areas of the southern Kherson region that were back under Ukrainian control following a recent counteroffensive, the deputy head of Zelenskiy's administration said.
"After a trip to the ... Kherson region, one thing became clear: our people there need a lot of help. The Russians not only killed and mined but also robbed all the cities and villages. There is practically nothing there," Kyrylo Tymoshenko said on Telegram.
A Reuters witness heard explosions in the centre of Kherson city on Friday morning and saw black smoke rising from behind buildings. Police blocked off access but the commotion did not seem to faze hundreds of people on the central square as they queued for humanitarian aid.
The General Staff of the Ukrainian Armed Forces said Russian forces redeployed on the east bank of the Dnipro River in Kherson region had shelled towns including Antonivka and Bilozerka on the west bank as well as Chornobaivka, which they had used as a depot for equipment.
Investigators in liberated areas of Kherson region had uncovered 63 bodies bearing signs of torture after the Russian forces left, Ukraine's interior minister said.
The Ukrainian parliament's human rights commissioner, Dmytro Lubinets, released a video of what he said was a torture chamber used by Russian forces in the Kherson region.
Separately, Yale University researchers concluded in a report backed by the US State Department that hundreds of people were detained or went missing in Kherson while it was under Russian control this year, and dozens might have been tortured.
Mass burial sites have been found in other parts previously occupied by Russian troops, including some with civilian bodies showing signs of torture.
Russia denies its troops deliberately attack civilians or have committed atrocities.
Russia has moved some troops from Kherson to reinforce its positions in the eastern Donetsk and Luhansk regions. Ukraine's military said Russian forces had fired shells at a series of towns in eastern and southern Ukraine.
In the first known high-level, face-to-face US-Russian contact since the invasion of Ukraine, CIA chief William Burns delivered a cautionary message this week during talks in the Turkish capital Ankara about the consequences for Moscow of any use of nuclear weapons.
Turkish President Recep Tayyip Erdogan told Russian leader Vladimir Putin in a phone call on Friday that the Ankara talks had helped to prevent "uncontrolled" escalation in the field.