Speaking before the UN Human Rights Council in Geneva, Volker Turk cautioned that the dangers long warned about in connection with autonomous weapons were rapidly materialising.

"We are seeing a global shift in how war is waged," he said.

"The UN has warned for many years against the development of lethal autonomous weapons. This reality is now upon us."

He pointed to the rapidly escalating use of drones in warfare, "creating a new circle of hell" in places like the Democratic Republic of Congo, Gaza, Israel, Lebanon and Myanmar.

In Ukraine, he highlighted how "relentless drone attacks have caused mass casualties and terrorised civilians".

And in Sudan, he said his office had documented that drone strikes had killed more than 1,000 civilians between January and May this year, while long-range drones had also destroyed aid convoys and vital energy infrastructure.

And with the rapid advances in artificial intelligence, experts have increasingly been sounding the alarm that humans could lose control of such weapons.

The UN rights chief said "the prospect of billion-dollar, AI-enabled weapons, brought down by billion-dollar, AI-enabled defensive shields, exposes the horror, emptiness, and futility of war.

"Autonomous weapons cannot become a licence for atrocity crimes."

Discussions have been running for a decade around a possible future treaty regulating the use of automated weapons, often referred to as killer robots.

Countries are due to decide later this year whether to launch full-on treaty negotiations.

Turk called on the international community to act to rein in the danger.

"States urgently need to consider the moral and legal questions this raises," he said, also calling on them to "agree on a common approach that protects civilian lives, and recommit to diplomacy and mediation.

"They must update legal frameworks to require human control and ensure accountability."