Nearly 43 years after the first recorded death by industrial robot in a Michigan auto plant, a new generation of autonomous machines threatens to take lives on an unprecedented scale.

So-called "killer robots" - weapons systems powered by artificial intelligence that identify and engage targets without human oversight - are rapidly moving from science fiction to reality. Countries around the globe are rushing to develop lethal autonomous weapons for the battlefield, raising alarms at the United Nations over their moral, ethical and legal implications.

As AI technology gallops ahead, experts warn these machines could decide to kill without accountability or human compassion.

"Delegating life-and-death decisions to machines crosses a red line for many people," said Bonnie Docherty, a lecturer at Harvard Law School. "It would dehumanize violence and boil down humans to numerical values."

The first autonomous weapons have already been deployed in regional conflicts from Libya to Nagorno-Karabakh. So-called "loitering munitions" hover above a battlefield scanning for targets, waiting to strike once an enemy is identified. Their degree of autonomy varies, but analysts say the technology is advancing at an exponential rate.

In November, 164 nations at the UN General Assembly voted to move forward on a potential global ban, despite opposition from major military powers like the United States, Britain and Russia. Previous efforts have faltered over disagreements on whether restrictions should be legally binding or voluntary.

But campaigners for an outright prohibition say the world can't afford to wait, with algorithmic bias and legal gray areas posing additional dangers beyond the moral quandary of machines dealing death. There are also fears that autonomous weaponry could dangerously escalate conflicts once unleashed.

"We believe legally binding rules are needed that prohibit certain kinds of autonomous weapons systems," Docherty said. "The use of these systems would undermine existing international law by falling into an accountability gap."

As the march toward sophisticated AI weapons systems accelerates, the UN faces a race against time in bringing them under international control. Allowing autonomous robots to determine who lives and dies might cross a final threshold in what it means to be human.