Local authorities said they discovered 25 torture camps in the area surrounding the eastern Ukrainian city of Kharkiv since its liberation from Russian occupation.
In the camps, Russian troops had detained and tortured civilians under inhumane conditions, among other things, regional police chief, Volodymyr Timoshko, has said in a Facebook post.
He said some of the prisoners had been subjected to electric shocks and others had had their fingers broken.
The area around Kharkiv was occupied by Russian troops for months.
They only withdrew at the beginning of September after a Ukrainian counteroffensive.
Since then, 920 bodies of civilians, among them 25 children, have been discovered in the liberated region, Timoshenko added.
“They were killed by Russian soldiers,” he said.
According to investigations by Ukrainian authorities, Russian forces have also committed war crimes in other occupied territories.
After the withdrawal of Russian units from the Kyiv suburb of Bucha, the bodies of more than 400 people were discovered there.
Most of them had suffered violent deaths. The investigation is ongoing.
Meanwhile, Russia said 63 soldiers were killed in Ukrainian missile strikes in the Donbas region of eastern Ukraine on New Year’s Eve, as Kiev reported a fifth consecutive night of mass drone strikes.
“The missiles hit temporary accommodation in Makiivka near Donetsk,” the Defence Ministry in Moscow said.
Earlier, the Ukrainian military reported that 400 Russian soldiers had been killed and 300 wounded.
It is very unusual for Moscow to confirm a high number of soldiers killed after an attack.
It is the highest number of deaths in one place cited by Russia itself in the war that Russia started in February.
The figure was nevertheless considered by many to be too low.
According to media reports, those killed are reservists who were called up in the course of the partial mobilisation ordered by Russian President, Vladimir Putin.
They are said to have gathered in the building for the new year’s celebration.
The Ukrainian military reportedly became aware of the site because of the high activity of mobile phone data traffic.
Unconfirmed reports said the building was next to an ammunition depot, which was why there were devastating explosions.
Meanwhile, Kiev Mayor, Vitali Klitschko, said the energy infrastructure had been damaged in the capital city after five consecutive nights of drone attacks throughout Ukraine.
This had led to power cuts that were also affecting the provision of heating.
However, the water supply was running normally, he said on Monday morning.
Colonel Vladislav Zelesnyov told the Ukrainian news agency RBK-Ukraina on Monday that the attacks were deliberately carried out at night and along the Dnipro river.
“Logically, not everything is visible in the sky at night,” he said.
He added that the flight path from the south along the Dnipro was also chosen to avoid Ukrainian air defences where possible.
Russian military bloggers reported that the areas targeted included Poltava, Kharkiv, Donetsk, Dnipropetrovsk, Mykolaiv and Kherson alongside Kiev, in the massive wave of attacks that started on Thursday.
Ukrainian President, Volodymyr Zelensky, meanwhile said he had information that “Russia is planning a long-term attack by Shahed drones,” saying that Russia wanted to use the drones to achieve attrition.
“But we must and will do everything to make this terrorist target fail like all others,” he said.
The Russian military used so-called kamikaze drones, which descend vertically on their target at the end of their flight.
The relatively slow Iranian-made drones are an easy target for air defence, but the large numbers of unmanned projectiles used and the constant airspace surveillance are a major challenge for Ukrainian air defence.
There was also the cost factor, a drone made of cheap parts has to be shot down with expensive weapons systems.
Russia has repeatedly reported drone attacks coming from Ukraine, with Gov. Alexander Bogomas saying one hit energy infrastructure in the Russian region of Bryansk near the border on Monday.
He said one town lost power but there were no casualties.
Later in the day, Russian state news agency TASS reported that two Ukrainian unmanned aerial vehicles were shot down over the naval port of Sevastopol in the Russian-occupied Crimean peninsula.
“Our air defences continued to repel the attacks,” Moscow-appointed governor, Mikhail Razvozhayev, was quoted as saying.
Sevastopol is the main base for the Russian Black Sea Fleet.
The port has been the target of Ukrainian drone attacks several times, most recently on Dec. 30.
