Moscow has a history of falsely accusing its enemies of attacks that could be defined as war crimes.
www.bbc.co.uk
In the BBC article they are ascribing it to ammonium nitrate released by ordnance hitting a farm building.
On another note find this assessment a little odd UK MoD:
"Russian bridging equipment has been in short supply throughout the conflict, slowing and restricting offensive manoeuvre." - they may have problems getting it to where it needs to be and/or they may assess that what they have is insufficient for a larger push beyond the Donbas but one of the reasons I thought this was likely going to lead to war this time was the large convoys of bridging equipment being moved to forward positions. They may have lost/had to abandon some of it when they pulled out of the north but there was still a lot being moved between Kursk and Belgorod compared to what has been sighted in Ukraine so far.