The UN is never unanimous in silence and never will be unanimous in anything, assuming we are talking of the general council, let alone the vestigial cold war security council (China is still commie, and Russia is pretend not, didn't you know?). What does evidence have anything to do with it?
Any such event (nuclear) will be denied by all the obvious culprits and any retaliation will be condemned by all the usual culprits, and all the usual sheep will buy whatever they have been told.
The only rational result will be that every one of the deniers will be be threatened with the same, but unfortunately that includes China and Russia these days.
Think they will be smart enough to change course? I don't know.
PS ever think what kind of world we would live in if China, Russia and, what the hell, throw in India and Pakistan would actually agree on putting petty dictators in their place? (Hey, I leave out France and Germany deliberately).
The Chinese are the doodoo's of the world these days in my opinion. They created N Korea, they protect and help Iran, they excuse Syria, then encourage Chavez, they love African dictators with mines, they make cheap Rolexes and they fill my mailbox (filtered) with imbecilic spam.
I try to find shirts I can afford that say anything other than made in China. Honest.
Russians next week. Stay tuned.