Looks like the military sources cited by Ukrainska Pravda was an official AFU statement from the general staff.
I think there’s no question that the plane has been downed by Ukraine. The only thing that’s not been confirmed is whether the IL-76 was carrying POWs (though, given the fact that it was flying over Belgorod, what else would it be carrying? The IL-76 has the radar cross-section of a whale), but delivery of POWs to Belgorod airport by IL-76 is standard practice according to previous prisoner exchanges.