Yes, it would violate treaties against the weaponization of space but I would lay even money on the idea that some country has already done this.
It only works as a deterrent if you break the treaty and everyone knows you've broken the treaty (whether you publicly admit it or not) but we aren't there afaik.
It could work if it gets to the point where 'only an idiot' wouldn't have broken the treaty, so you can just assume everyone has, because the idea is fairly obvious, the technology is easy, and there's not any other good options. Or if a rogue state does it or something like it, then you can assume the US and Russia have done it or will be doing it shortly.
at best it's just an "are you feeling lucky?" situation unless you publicly prove it