Putin has complained that NATO is waging a proxy war in Ukraine.
Poor baby. He's certainly right, though I would say that NATO's doing it with at least one fist timed behind its back.
But Lavrov's words notwithstanding, I don't think even Putin thinks there has been justification for using nukes.
Doesn't mean he won't, but if he is going to insist on telling people that he is winning, then his using nukes is problematic for more than just those on the receiving end of it.
I hope he won't, but I have no faith in him.