Some militaries are working on drones that are completely controlled by AI. These would make their own decisions about firing. As far as we know, autonomous drones have been used to fire on people once already.
The people behind the land mine treaty are working with the UN to try to put in place a treaty that would ban killer robots. This effort has had many backers including Stephen Hawking. I also back it because these giant terrible international bodies do actually help curtail the bad behaviour of states. The stakes on this are incredibly high.