The Russian army reported 40 dead and 75 wounded in the strike on Olenivka prison, while the pro-Russian separatist authorities in the Donetsk region mentioned death tolls of 47 and 53.
Ukrainian forces "fired on the prison where members of the Azov battalion are being held, using American projectiles from the Himars system", said the Russian Investigative Committee, Russia's main investigative body.
The Azov regiment, which Moscow accuses of being a neo-Nazi formation, distinguished itself in the defense of the city of Mariupol, in southeastern Ukraine, against the Russian army.
After long weeks of siege and resistance at the Azovstal steel site in Mariupol, some 2,500 Ukrainian fighters surrendered in May. The Russian authorities had indicated that they would be imprisoned in Olenivka.
"This outrageous provocation aims to scare Ukrainian soldiers and dissuade them from surrendering," the Russian Defense Ministry said.
But Ukraine quickly denied having targeted civilian infrastructure or prisoners of war, stressing that the army "fully adheres to the principles and standards of international humanitarian law".
The Ukrainian general staff in return accused the Russian army of being behind this "targeted artillery bombardment", in order to "accuse Ukraine of having committed war crimes and cover up the torture of prisoners and the executions they perpetrated there".
Russian public television broadcast images presented as those of the charred barracks and the tangles of destroyed metal beds. She showed blurry images of what appear to be human bodies.
AFP was unable to verify all of these statements from independent sources.
- Bus stop hit -
Also on military ground, at least five people were killed and seven injured in a Russian strike that hit a bus stop in the Mykolaiv region of southern Ukraine, according to regional governor Vitaly Kim.
He accused the Russian forces of "bombarding the city during the day, when everyone is going about their business".
And at least eight people, according to the Ukrainian presidency, have been killed and 19 injured in the past 24 hours in the Donetsk region. This region, in the Donbass mining basin, has been partly controlled since 2014 by pro-Russian separatists and Moscow is seeking to conquer it in full.
In the Kharkiv region in the northeast, at least one person was killed and seven others injured, according to the same source.
The Ukrainian army for its part destroyed a train station in Brylivka, a village in the southern occupied region of Kherson, where the Ukrainians launched a counter-offensive, in order to complicate supplies for the Russian army, said the local MP Serguii Khlan.
Separately, the life sentence handed down to a Russian soldier in May for killing a civilian in Ukraine was reduced to 15 years in prison on appeal by a kyiv court.
Sergeant Vadim Chichimarine, 21, admitted to shooting dead Oleksandre Chelipov, a 62-year-old civilian, in the northeast of the country during the first days of the Russian army's invasion of Ukraine on February 24 . Pleading guilty, he was sentenced on May 23 for war crimes and premeditated murder.
- Imminent grain exports -
On the grain front blocked in Ukraine since the start of the war, exports could resume "in the coming days", according to kyiv.
President Zelensky visited the Black Sea port of Chornomorsk on Friday to oversee a first shipment of grain to a Turkish ship, under the terms of an agreement reached on July 22 with Russia.
"We are fully prepared. We have sent all the signals to our partners, the UN and Turkey, and our military guarantees the security situation," Zelensky said. According to him, kyiv is only waiting for a "signal" from Ankara and the UN, guarantors of the agreement, to "begin".
Ukraine, like Russia, are among the world's largest grain exporters. kyiv says it wants to sell some 20 million tonnes worth around $10 billion under the deal to ease a global food crisis that has seen prices soar in some of the world's poorest countries. world.
In the energy field, Saudi Crown Prince Mohammed bin Salman and French President Emmanuel Macron wanted to "intensify cooperation" to "mitigate the effects in Europe, the Middle East and the world" of the war in Ukraine, according to the French presidency.
Since the Russian invasion, Western countries have been trying to convince Saudi Arabia to open the floodgates in order to relieve the markets. Rising oil prices are fueling inflation in the United States, which has reached 40-year highs.
