Japan, the United States and other countries have blocked any advancement in U.N. talks toward legally binding measures to ban and regulate the development and use of lethal autonomous weapon systems.

The Sixth Review Conference of the Convention on Certain Conventional Weapons ended Friday in Geneva without progress, failing to reflect eight years of work and leaving countries and nongovernmental organizations that have called for legally binding rules expressing disappointment.

Also referred to as "killer robots," autonomous weapons are artificial intelligence-powered weapons using facial recognition and algorithms.

Once activated, the weapons can select and attack targets without the assistance of a human operator. They pose ethical, legal and security risks.

Japan is opposed to any start of negotiations on a legally binding instrument, as are the United States, Australia, South Korea, India, Russia and Israel, given that autonomous weapons are thought to provide military advantages such as swifter reactions and reduction of troops' direct exposure on the battlefields.

"Japan has the position that discussions must continue, but they are against any attempt to start negotiations on a legally binding instrument," a diplomatic source said.

Autonomous weapons are known to be in development, but are not yet in use. A U.N. document published in March reported on the alleged first autonomous drone attack in Libya.

According to the NGO Stop Killer Robots, countries such as the United States, China, Israel, South Korea, Russia, Australia and Britain are already developing autonomous weapons.

While diplomatic talks toward concrete measures are in a stalemate, technology required to produce these weapons is being developed very quickly.

China, which made few interventions during the five-day talks in the Swiss city, said it is not against legally binding measures "based on an agreement to be reached on definitions."

Discussions showed common definitions of the complex weapon systems relying on ever evolving technologies will be difficult to reach.

China said it has submitted a position paper on regulating the military application of AI.

A Chinese representative said it was the first time Beijing has put forward a comprehensive and systematic proposal on the security governance of AI within the framework of the U.N. Convention on Certain Conventional Weapons.

NGOs and AI and robotics experts, as well as a large number of countries including Austria, Chile, Ireland and New Zealand, have been pushing for the start of negotiations on legally binding rules.

They expressed "deep disappointment" at the outcome of the talks, which basically only mandate the group of experts to continue discussions without concrete goals.

Mary Wareham, arms advocacy director for Human Rights Watch, an international NGO, said the outcome is "a completely inadequate multilateral response" given the urgent need for new international law on autonomous weapons.

"Military powers Russia & United States are primarily responsible for this shameful result," Wareham wrote on Twitter.