If it is a rouge unit(s) , not accepting the terms or orders from their government , the talks should proceed if both are willing , as those units are now traitors to their nation . If they are not obeying Kiev , then that should be a wake up call to that government to do a purge ………….you cant tolerate that in wartime . If a tactical nuke was used , there should be reports of radiation coming forward , on the other hand , there are a lot of cases where conventional explosives look very much like a nuke . Depends on what went up , something was obviously concentrated in that area . If it was a nuke and we did it , expect our allies to turn against us , that is something you just dont do .