Russia, Ukraine dispute cause of explosion killing POWs

 ISW:

A kinetic event killed and wounded scores of Ukrainian POWs in Russian-occupied Olenivka, Donetsk Oblast, on July 28.[1] Ukraine and Russia are blaming each other for the attack and available visual evidence appears to support the Ukrainian claim more than the Russian, but ISW cannot independently assess the nature of the attack or the party responsible for it at this time. The Russian Defense Ministry asserted that Ukrainian forces deliberately struck the Olenivka pre-trial detention center holding Ukrainian POWs including Azov Regiment servicemen using Western-provided HIMARS, killing at least 40 and wounding 75 POWs.[2] Kremlin-sponsored news outlet “RIA Novosti” published videos of the detention center, which showed fire damage but not the sort of damage that a HIMARS strike would likely have caused.[3] RIA Novosti also released footage of HIMARS missile fragments but provided no evidence that the fragments were recovered at Olenivka.[4] Luhansk People’s Republic (LNR) Ambassador to Russia Leonid Miroshnik claimed that Ukrainian forces struck the pre-detention center to eliminate the evidence of Ukrainian surrenders and prevent POWs from speaking out against the Ukrainian government.[5]

The Ukrainian General Staff said that Russian forces conducted the attack as a false flag operation to cover up Russian war crimes, disrupt the supply of Western weapons, discredit Ukrainian forces, and stoke social tensions within Ukrainian society.[6] The Ukrainian General Staff stated that a deliberate explosion occurred near the newly-constructed penal colony, to which Russian forces had transferred Ukrainian POWs a few days earlier. The Ukrainian General Staff also noted that Ukrainian analysis of the damage to the building, intercepted phone conversations between Russian servicemen, the lack of reported shelling in Olenivka, and the absence of casualties among Russian personnel serving at the penal colony all point to a Russian deliberate “terrorist act” as the cause of the incident.[7] The Ukrainian Main Military Intelligence Directorate (GUR) accused Wagner Group head Yevgeny Prigozhin of ordering the “terrorist act” without consulting with the Russian Defense Ministry, to conceal the embezzlement of funds allocated for the maintenance of Ukrainian POWs before an official inspection on September 1.[8] The Ukrainian Office of the General Prosecutor reported that the explosion killed at least 40 and wounded 130 Ukrainian POWs.[9]

ISW is unable to assess the nature of the event or the party responsible for it with any confidence at this time. We will update our assessment as more information becomes available.
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I suspect the lack of Russian casualties may be significant in determining who was responsible for the explosion.  As noted by ISW, the damage does not suggest a HIMARS weapon was used.  Ukraine has also been rather adept at intercepting Russian telephone communications and in many cases giving those intercepts to the media especially when Russian troops discuss morale problems and disagreement with the war efforts.