I suspect it is more about keeping the populace frightened and malleable by scaremongering about Western nuclear attacks - if they think they are under threat of WW3 they are far less likely to be protesting in the streets.
Absolutely agree. It is an "Enemy at The Gates" message. They are struggling to find new cannon fodder, support for the war could be waning (from videos and tel calls being released), problems caused by the sanctions.
What better way to mobilise the Russian populace behind the war than saying the big bad Nato and Nazis are once again threatening Moscow.
It would seem that the Russian populace is still fighting WWII in their psyche - so start with the big brother messaging to really get things moving.