Paris - A group of top tech leaders, including British scientist Stephen Hawking and Apple co-founder Steve Wozniak, on Tuesday issued a stern warning against the development of so-called killer robots.Autonomous weapons, which use artificial intelligence to select targets without human intervention, have been described as "the third revolution in warfare, after gunpowder and nuclear arms," around 1 000 technology chiefs wrote in an open letter."The key question for humanity today is whether to start a global AI [artificial intelligence] arms race or to prevent it from starting," they wrote."If any major military power pushes ahead with AI weapon development, a global arms race is virtually inevitable," the letter continued.The idea of an automated killing machine - made famous by Arnold Schwarzenegger's Terminator - is moving swiftly from science fiction to reality, according to the scientists."The deployment of such systems is - practically if not legally - feasible within years, not decades," the letter said.The scientists painted the Doomsday scenario of autonomous weapons falling into the hands of terrorists, dictators or warlords hoping to carry out ethnic cleansing."There are many ways in which AI can make battlefields safer for humans, especially civilians, without creating new tools for killing people," the letter said.In addition, the development of such weapons, while potentially reducing the extent of battlefield casualties, might also lower the threshold for going to battle, noted the scientists.The group concluded with an appeal for a "ban on offensive autonomous weapons beyond meaningful human control."Open letterThe letter was presented at the opening of the 2015 International Joint Conference on Artificial Intelligence in Buenos Aires.Elon Musk, the billionaire co-founder of PayPal and head of SpaceX, a private space-travel technology venture, also urged the public to join the campaign."If you're against a military AI arms race, please sign this open letter," tweeted the tech boss.Authorities are gradually waking up to the risk of robot wars.Last May, for the first time, governments began talks on so-called "lethal autonomous weapons systems."In 2012, Washington imposed a 10-year human control requirement on automated weapons, welcomed by campaigners even though they said it should go further.There have been examples of weapons being stopped in their infancy.After UN-backed talks, blinding laser weapons were banned in 1998, before they ever hit the battlefield.