Cinema-goers will be shocked this week to see an advertisement selling AK47 machine guns, alongside the ads for cars and soft drinks. It's a spoof by Amnesty International, sending up TV shopping channels to draw attention to the appalling ease with which weapons are bought and sold around the world. But the reality is far more shocking.

As a human rights campaigner, I've visited countless countries where people suffer terrible abuses. Women raped at gunpoint during the conflict in the Balkans, police killings of street children in Brazil, the horrors committed during conflicts in central Africa. Behind so many of these atrocities is one common factor: the gun. Around the world, arms facilitate abuse. Torture, "disappearances", rape, all take place at gunpoint. And behind that gun is the arms dealer, profiting from a trade that's barely regulated and spiraling out of control.

States have a right to bear arms and to protect their citizens, so trade in arms is inevitable. But for such an enormous and lethal business there is a startling lack of controls to ensure that those weapons don't go to people who will abuse them. One person dies every minute as a result of armed violence - half a million men, women and children every year. Conflict fuels poverty as vital resources are wasted on expensive military hardware; and at a local level terrified people are unable to go about their ordinary, working lives.

Yet some people are making big money from the spiraling violence. The global arms trade is enormous, with about $21billionn of authorized exports every year. Most of the sales are from the richest and most powerful nations. From 1998 to 2001 the US, Britain and France earned more from arms sales to the developing world than they gave in aid.

So what is the answer? An international arms trade treaty would make it illegal to sell arms to countries where they could be used to abuse human rights or break international humanitarian law. It would be legally binding, replacing the existing "gentlemen's agreements" that are conveniently forgotten when it is expedient to do so. And it would provide a set of common standards to stop gunrunners exploiting loopholes in national laws.

Such a treaty has been drafted by campaigners and already has the support of over 40 countries, including the UK, and the Defense Manufacturers Association, the voice of the British arms industry. They rightly recognize the need for a set of common standards to govern the global arms trade.

Of course, such a treaty would only stop the flow of arms into countries where they do such damage. It would not reduce the enormous number of arms that already exist: nearly 640 million small arms. At the end of the contra war in Nicaragua, where I was born, thousands of weapons remained in the hands of "civilian" rebels and army personnel. While I was making a documentary on the demobilization of the contras, weapons were everywhere. It's difficult to convince people that to normalize an aggravated situation arms need to be destroyed on both sides. So we also need action to drain the existing pool of arms, and provide people with security so they do not need weapons for self-protection.

But there's no point draining the pool of arms if we don't stop unscrupulous dealers flooding conflict zones with more weapons. Governments must recognize that arms proliferation is one of the main drivers of human rights abuse and poverty, and take action. The UN is meeting in June to discuss the issue, but it will only act if put under pressure. The international community must acknowledge that the reality of armed violence is even more shocking than that pictured on our cinema screens.

Bianca Jagger is a human rights campaigner