The ATT would prohibit states from transferring conventional weapons to countries when they know those weapons would be used to commit or facilitate genocide, crimes against humanity or war crimes.
At least 500,000 people die every year on average and millions more are displaced and abused as result of armed violence and conflict.
Countries from every region in the world signed the historic treaty at the first opportunity -- including France and the UK with Germany expected to sign later today -- three of the world's major arms exporters.
The US -- by far the world's largest arms producer and exporter -- said it plans to sign the treaty soon.
"The ink is barely dry on today's signatures but the commitment of the world's arms exporting powers for the ATT is already coming under question by the worsening situation in Syria," said Brian Wood, Head of Arms Control and Human Rights at Amnesty International.
"Declarations of support for the ATT would ring hollow if decisions to send arms to Syria and elsewhere are inconsistent with the principles of the treaty. This is a critical test for governments to demonstrate they are serious about implementing a treaty that puts human beings and their security first."
Under the treaty, it's clear that the Syrian government cannot receive arms given its record of deliberately targeting civilians.
There is currently a substantial risk that arms supplied to Syrian opposition groups would be used to commit or facilitate more human rights abuses.
Whilst this substantial risk remains no arms should be supplied.
The signing ceremony took place just two months after the UN General Assembly voted overwhelming to adopt the treaty text, with 155 states in favour and only three against (Iran, North Korea and Syria). While Russia, China, Egypt and India were among 23 countries to abstain.
The ATT now requires ratification by fifty states before it enters into force.
"The fact we have reached this point is a truly historic achievement. With 62 countries signing and many more already indicating their intention to sign - there is a now gathering momentum to ensure the treaty is in force by the end of 2015 thereby helping protect human rights and save the lives of millions," said Wood.
Amnesty International has campaigned since the early 1990s to achieve robust, legally binding global rules on international arms transfers to stem the flow of conventional arms and munitions that fuel atrocities and abuse.
Millions of people around the world called on governments to agree a treaty with the potential to protect lives.
Amnesty International and its partners continue to push for governments to sign, ratify and strictly implement the treaty as soon as possible.
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