More than 60 countries on Monday signed a landmark conventional arms trade treaty, but the United States held back from joining the first wave of signatories while Russia and China are expected to stay out of the accord.

The UN-brokered treaty is the first covering weapons of any kind for more than a decade and aims to bring transparency and protection of human rights into the often dubious $85 billion-a-year global trade.

UN Secretary General Ban Ki-moon said the treaty will "put an end to the 'free-for-all' nature" of weapons dealing and make it harder for warlords, pirates and terrorists to get arms."

The treaty covers tanks, armored combat vehicles, large-caliber artillery, combat aircraft, attack helicopters, warships, missiles and missile launchers, as well as the vast trade in small arms.

Countries that ratify the treaty would have to evaluate before making a deal whether it risks breaching an international embargo, violates human rights law, or could be used by terrorists or criminals.

The opening of signatures was described as an "extremely important milestone" by ministers and other representatives of Argentina, Australia, Britain, Costa Rica, Finland, Japan and Kenya which sponsored the first 2006 UN resolution calling for treaty talks.

Argentina was the first of 63 countries to sign the treaty on the first day.

Fifty ratifications are needed for the treaty to come into force. Finland's Foreign Minister Erkki Tuomioja said this could be done within a year.

The UN General Assembly passed the treaty in April when 154 countries voted in favor, but Syria, North Korea and Iran voted against and Russia, China, Egypt and India were among 23 countries to abstain.

Russia and China are not expected to join the treaty any time soon.

Among major arms exporters, Britain, France and Germany all signed the treaty on the first day.

Germany's Foreign Minister Guido Westerwelle called the treaty a "historical breakthrough".

But he added that the treaty "can only make a real difference if it is fully implemented on a global scale. Our first task is to push for its early entry into force." Westerwelle said the German parliament will start work on a draft ratification law this week.

Britain's deputy foreign minister Alistair Burt said doubters of the treaty were now under pressure to join. "The force behind so many states wanting to conclude an arms trade treaty after so long meant something. The world is now different," he told reporters.

"France hopes for a rapid entry into force of the Arms Trade Treaty, a major step for human rights," said France's Foreign Minister Laurent Fabius in a statement.

The United States, the world's biggest exporter of arms and ammunition, played a key role in getting the treaty passed but was not among the first signatories.

"The United States welcomes the opening of the Arms Trade Treaty for signature, and we look forward to signing it as soon as the process of conforming the official translations is completed satisfactorily," said US Secretary of State John Kerry in a statement.

He said many of the controls in the treaty were already enforced in the United States. But Kerry added that "the treaty is an important contribution to efforts to stem the illicit trade in conventional weapons."

The US administration has faced pressure from the domestic arms lobby over the treaty but Kerry said it "will not undermine the legitimate international trade in conventional weapons, interfere with national sovereignty, or infringe on the rights of American citizens."

Brian Wood, Amnesty International's specialist on arms control, said "the United States could sign soon but ratification will be a bigger hurdle given the positions in Congress."

He added that China could still be convinced to join the treaty but Russia and India were unlikely to sign.