Russia and Ukraine accused one another over the shelling of a prison in separatist-held eastern Ukraine that killed at least 40 Ukrainian prisoners of war.  “Ukrainian security forces fired [U.S.-supplied long-range missile systems] HIMARS rockets at a pre-trial detention center near Olenivka tonight,” Russia’s Defense Ministry said in a statement carried by state news agencies. It said Ukrainian prisoners of war — including members of the Azov Regiment who surrendered in May after defending the port city of Mariupol from within the besieged Azovstal steel plant — were held at the Olenivka prison. Russia’s Defense Ministry said 40 Ukrainian POWs were killed and 84 others wounded.Authorities in the separatist Donetsk People's Republic placed the death toll at 53, adding that no prison guards were injured or killed.Ukraine’s military denied Russia’s claim later Friday, accusing Russian forces of directing artillery fire at the Olenivka prison “to hide the torture of prisoners and executions committed on the orders of the occupying administration.”Ukraine's Foreign Minister Dmytro Kuleba echoed the accusations."Russia has committed another petrifying war crime by shelling a correctional facility in occupied Olenivka where it held Ukrainian POWs.

I call on all partners to strongly condemn this brutal violation of international humanitarian law and recognize Russia a terrorist state," Kuleba wrote on Twitter.Denis Pushilin, head of the Donetsk People’s Republic, claimed without evidence that the attack was a deliberate attempt to keep the Ukrainian soldiers from “testifying” for Donetsk’s “war crimes trial” that Kyiv decries as a sham.The Russian and separatist accusations come amid Ukraine’s active counteroffensive to retake two occupied southern regions.Ukrainian soldiers captured during five months of fighting are being held in Russian-controlled territories, with independent media reporting that some of them had been transferred to Moscow’s notorious Lefortovo prison.AFP contributed reporting.