Militaries across the world are said to be 'very excited' about machines that could deployed alone in battle, sparing human troops from dangerous situations.
The U.S. is leading development in such 'killer robots', notably unmanned drones often used to attack suspected militants in Pakistan, Yemen and elsewhere.
Comment: The truth of the matter is that US drones have been terrorizing and killing innocent civilians, women and children, in these countries.
Raytheon's Phalanx gun system, deployed on U.S. Navy ships, can search for enemy fire and destroy incoming projectiles by itself.
The Northrop Grumman X47B is a plane-sized drone able to take off and land on aircraft carriers, carry out air combat without a pilot and even refuel in the air.
But perhaps closest to the Terminator-type killing machine portrayed in Arnold Schwarzenegger's action films is a Samsung sentry robot already being used in South Korea.
The machine is able to spot unusual activity, challenge intruders and, when authorised by a human controller, open fire.
The warnings come from a new report by Human Rights Watch, which insists that such Terminator-style robots are banned before governments start deploying them.
The report, dubbed Losing Humanity and co-written by Harvard Law School's International Human Rights Clinic, raises the alarm over the ethics of the looming technology.
Calling them 'killer robots,' it urges 'an international treaty that would absolutely prohibit the development, production, and use of fully autonomous weapons.'
Such machines would mean that human soldiers could be spared from dangerous situations, but the downside is that robots would then be left to make highly nuanced decisions on their own, the most fraught being the need to distinguish between civilians and combatants in a war zone.
'A number of governments, including the United States, are very excited about moving in this direction, very excited about taking the soldier off the battlefield and putting machines on the battlefield and thereby lowering casualties,' said Steve Goose, arms division director at Human Rights Watch.
While Goose said 'killer robots' do not exist as yet, he warned of precursors and added that the best way to forestall an ethical nightmare is a 'preemptive, comprehensive prohibition on the development or production of these systems.'
'If a robot goes wrong, who's accountable? It certainly won't be the robot' Noel Sharkey, University of Sheffield
The problem with handing over decision-making power to even the most sophisticated robots is that there would be no clear way of making anyone answer for the inevitable mistakes, said Noel Sharkey, professor of robotics at University of Sheffield.
'If a robot goes wrong, who's accountable? It certainly won't be the robot,' he said.
'The robot could take a bullet in its computer and go berserk. So there's no way of really determining who's accountable and that's very important for the laws of war.'
Now watch a video demo of Samsung's machine gun sentry robot: