Recently, I asked the German government which promised to support an international ban on autonomous weapon systems how this initiative is developing. They referred to ongoing multilateral discussions at the Geneva UN Convention on Certain Conventional Weapons (CCW) where an informal working group prepared a Report on Lethal Autonomous Weapon Systems (LAWS), which I recommend for your attention.
The window of opportunity is closing, though. There is not much time left for an international agreement to stop killer robots. As was mentioned in the now famous Open Letter Against Autonomous Weapons from July 2015, they are only years away, not decades. This has been confirmed recently by a high ranking military official from Israel.
I elaborate a bit more on the topic in this article (in German).