Is Putin a valid military target in this war? What about Moscow based senior political and governmental figures with roles related to the war effort?

Putin apparently believes the head of state of Ukraine is a valid target, suitable to be dispatched by any means. Or at least that seems to be a reasonable interpretation of some reports. Doesn't that imply that Putin himself must be, as well?

What about other senior Russian figures, even if behind a desk in Moscow? Politicians, or those enabling the war effort?

How far across the Russian political and governmental landscape, would count as valid targets?

And under international law, who is entitled to act on that status? Just Ukraine and formally declared allies, or can any third party individual/group/state declare alignment with Ukraine and become a valid actor?