Killer robots being developed by the US military "will leave humans utterly defenceless", an academic has warned.
Two programmes commissioned by the US Defense Advanced Research Projects Agency are seeking to create drones which can track and kill targets even when out of contact with their handlers.
Writing in the journal Nature, the professor of computer science at the University of California, Berkley, Stuart Russell, said the research could breach the Geneva Convention and leave humanity in the hands of amoral machines.
"Autonomous weapons systems select and engage targets without human intervention; they become lethal when those targets include humans," he said.
"In my view, the overriding concern should be the probable endpoint of this technological trajectory.
"Despite the limits imposed by physics, one can expect platforms deployed in the millions, the agility and lethality of which will leave humans utterly defenceless. This is not a desirable future."
The robots, called Laws - lethal autonomous weapons systems - are likely to be armed quadcopters or mini-tanks that can decide without human intervention who should live or die.
Last year Angela Kane, the UN's high representative for disarmament, said killer robots were just a "small step" away and called for a worldwide ban.
Russell said: "Laws could violate fundamental principles of human dignity by allowing machines to choose who to kill."