Anti-personnel land mines are illegal under international law as per the Ottowa Treaty 1997, to which Ukraine is signatory.

Russia is one of the non-signatories, and during the war Ukraine has decided to deploy land mines, but as a signatory this is illegal under international law. Ukraine has not yet withdrawn from the treaty so is eventually liable to prosecution for war crimes on this count as well. This would barr them from entry into the EU, for example.

International law is not a matter of what is convenient at the time. It is a commitment. This war is rapidly exploring new frontiers of killing, and it is absolutely essential that those actions are held to account for future posterity. Otherwise there is no such thing as a war crime, and it just comes down to who is willing to debase themself to the greatest extreme.