This week at the United Nations in Geneva, governments for the first time debated what to do about weapons that - once activated - would be able to select and engage targets without further intervention by a human. While it is good news that no country said 'bring them on', the challenge is how to nip the idea in the bud - before it's too late.

These fully autonomous weapons, sometimes called 'killer robots', do not exist yet. But already many robotic systems with various degrees of autonomy and lethality are being developed or used by nations with high-tech militaries such as the United States, China, Israel, South Korea, Russia, and the United Kingdom. It is clear that these and, perhaps, other countries are moving toward systems that would give full combat autonomy to machines.

Over the last decade, the expanded use of unmanned armed vehicles or drones has dramatically changed warfare; bringing new humanitarian and legal challenges. Imagine weapons that would be able to select and attack targets without any meaningful human intervention. The issue has been placed on the agenda of the UN Human Rights Council with the presentation of a report on lethal autonomous robotic weapons by Christof Heyns, a South African lawyer.

Professor Heyns is the UN special rapporteur on extrajudicial, summary or arbitrary executions for the Office of the High Commissioner for Human Rights. The UN report describes multiple moral, ethical, legal, policy, technical, and other concerns with respect to these weapons. Its recommendations include a call for an immediate moratorium on lethal autonomous robotic weapons and for countries to work for an international agreement to address the concerns identified in the report.

Until this week, only one country had publicly articulated its views on this issue. In November 2012, the US Department of Defence issued a directive that for now requires a human being to be "in-the-loop" when decisions are made about using lethal force. For up to 10 years, the directive generally allows the Defence Department to develop or use only fully autonomous systems that deliver nonlethal force - unless department officials waive the policy at a high level.

In effect, the directive constitutes the world's first moratorium on lethal fully autonomous weapons. While a positive step, a moratorium is not a comprehensive or permanent solution to the potential problems posed by fully autonomous systems. Policies of self-restraint, while helpful, may also be hard to sustain if other nations begin to pursue and deploy fully autonomous weapons systems.

This is why we at Human Rights Watch have joined with other non-governmental organisations to form the Campaign to Stop Killer Robots, a new international coalition of civil society groups that is working to pre-emptively ban weapons that would be able to select and attack targets without any human intervention. This prohibition should be achieved through an international treaty, as well as national laws and other measures, to enshrine the principle that decisions to use lethal force against a human being must always be made by a human being.

When the UN report was delivered to the Human Rights Council on Thursday, representatives from 26 countries provided their views on lethal autonomous robotic weapons in addition to the European Union and other regional bodies. All agreed that this is an issue of concern that must be addressed in a timely fashion. Many asked when, where and how this challenge could be tackled. Perhaps most important, no state asked why action is needed and defended the status quo. There are many questions to be addressed when it comes to this new issue and now is time for governments, UN agencies, the International Committee of the Red Cross and NGOs to start working together to address them.

A starting point would be to agree that humans should never delegate to machines the power to make life-and-death decisions on the battlefield. It is in the interest of America, the UK and other nations to develop global standards to prohibit these kinds of weapons. It is possible to halt the slide toward full autonomy in weaponry before moral and legal boundaries are crossed but only if we work together and start to draw that line now. As the UN report warns, "If left too long to its own devices the matter will, quite literally, be taken out of human hands."