Russia pounded Ukraine's energy facilities again on Thursday as the first snow of the season fell in Kyiv.
Explosions were heard in several parts of the country, including the southern port of Odesa, the capital Kyiv and the central city of Dnipro, and civilians were urged to take shelter as air raid warnings sounded.
Targets included the huge Pivdenmash missile factory in Dnipro, Prime Minister Denys Shmyhal said.
"Missiles are flying over Kyiv right now," he said early on Thursday, according to Interfax Ukraine news agency. "Now they are bombing our gas production [facilities], they are bombing our enterprises in Dnipro and Pivdenmash."
Light snow on Thursday dusted the capital, where the temperature fell below freezing.
The city’s military administration said air defences had shot down at least two cruise missiles and five Iranian-made exploding drones.
At least four people were killed and more than two dozen wounded in the drone and missile strikes, including one that hit a residential building, authorities said.
The attacks came as Ukrainian investigators in the recently liberated Kherson region uncovered dozens of bodies displaying signs of torture, the country’s Interior Minister said.
Sixty-three bodies were discovered with signs of abuse after Russian soldiers retreated, Denys Monastyrsky told national TV networks in Ukraine.
More than 430 instances of war crimes had been detected during Russia's occupation, he said. Eleven places of detention had been discovered, including four where torture had been used.
"Now, 63 bodies have been discovered in Kherson region, but we must understand that the search has only just started so many more dungeons and burial places will be uncovered,” Mr Monastyrsky said.
"Investigators are currently examining them and setting down every instance of torture. Exhumations are also taking place of the bodies of those who were killed.”
Andriy Kovalenko, a prosecutor in the Kherson regional prosecutor's office, told The New York Times that testimony had been gathered on 800 detentions by Russians in the region.
Forms of abuse included electric shocks, beatings with plastic or rubber nightsticks and suffocation by pinching the breathing hose on a gas mask placed over a prisoner's head.
Ukrainian and international investigators say Russian troops have been committing war crimes in occupied areas since Moscow's invasion of Ukraine in February.
Russia denies that its soldiers target civilians or have committed atrocities.
But mass burial sites have been found in other areas previously occupied by Russian troops, including some with civilian bodies showing signs of torture.
Russian forces left parts of Kherson region last week. The area was one of the first areas seized by Russia.
President Volodymyr Zelenskyy in a nightly video address said investigators had uncovered more than 400 crimes in Kherson.
He said the Russian Army had left behind corpses, broken infrastructure and landmines in what he described as "the same savagery it did in other regions".
Mr Zelenskyy has rebuffed the conclusion of preliminary investigations into the blast on Tuesday at a grain plant in Poland near the Ukrainian border, which suggested it was caused by a Ukrainian anti-aircraft missile.
"From the information that we and our allies have, it was an S-300 rocket made in the Soviet Union, an old rocket, and there is no evidence that it was launched by the Russian side," Polish President Andrzej Duda said.
Nato Secretary General Jens Stoltenberg said "it is highly likely that it was fired by Ukrainian anti-aircraft defence".
The old type was being used by both Russia and Ukraine.
The Nato chief said Russia, not Ukraine, was to blame for starting the war by invading in February and launching scores of missiles on Tuesday that triggered Ukrainian defences.
"I have no doubt that it was not our missile", Mr Zelenskyy told Ukrainian media on Wednesday.
He said he based his conclusion on reports from Ukraine's military which he "cannot but trust".
The incident occurred during Russia's barrage of missiles unleashed on cities across Ukraine, targeting its energy grid and prolonging power blackouts for millions, in what Ukraine called the most intense bombardment of the nine-month war.
Mr Zelenskyy said late on Wednesday that technicians had worked non-stop to restore electricity to households.
"We are talking about millions of customers," Mr Zelenskyy said. "We are doing everything we can to bring back power. Both generation and supply."
Speaking on Radio 4's Today show on Thursday morning, Oleksandra Azarkhina, Ukraine’s Deputy Minister of Infrastructure, said 40 per cent of the country's energy infrastructure had been destroyed by Russia.
"So we are trying to repair everything, replace everything but more and more capabilities are being targeted," she said.
"It’s impossible if we are alone here. But if we are acting together, it’s possible to re-establish normality as soon as possible."
She said the issue over the missile strike on Poland would soon be resolved.
"We do have communication with our allies," she said. "I am sure we will find the common ground and find out what the truth is. We are still waiting for the outcome of the investigation, so we will see. But of course we are relying on our army and the communication they are providing."
Ukraine has said that its air defences have knocked out many of the missiles and drones fired in the past few weeks.
"This morning Russia launched another missile barrage at Ukraine’s critical infrastructure," Foreign Ministry spokesman Oleg Nikolenko said.
"[Russian President Vladimir] Putin wants to deprive millions of people of electricity and heating, amid freezing temperatures. Send Ukraine more air and missile defence systems to avert this tragedy. Delays cost lives."
Elsewhere, Ukraine’s Infrastructure Ministry on Thursday confirmed a Black Sea grain project would be extended for 120 days.
The UN-backed agreement on July 22 allowed grain shipments to resume from certain Ukrainian ports on the Black Sea, leading to about 10 million tonnes being transported to rein in world food prices.