that's why and when he said, he's not bluffing and if needed, Russian military doctrine allows first nuclear strike if Russian Federation is jeopardized from outside aggressors

my bet is, that if Ukraine will keep on attacking, Putin may, but i hardly believe, send/attack with a tactical nuke some unimportant city as a message, and demand complete surrender of Ukraine's army

or, more likely, if Ukraine will keep attacking these territories, Putin will now with these newly regruted, mobilized forces, together with Belarus, go full out attack on Kiev and complete conquest of entire country, most likely hhh