US Secretary of State John Kerry signed the Arms Trade Treaty on Wednesday, saying it was a "significant step" toward preventing terrorists from obtaining conventional weapons and keeping the world safe.
The United States now joins 90 other nations that have signed the treaty that regulates global arms trading, although there is strong resistance to it in the Senate, which has final say on approving the agreement.
US lawmakers have said the treaty could lead to new gun control measures, but Kerry insisted it protects Second Amendment rights.
More from GlobalPost: UN Arms Trade Treaty ready for signatures, but will US sign?
"This is about keeping weapons out of the hands of terrorists and rogue actors," Kerry said. "This is about reducing the risk of international transfers of conventional arms that will be used to carry out the world's worst crimes. This is about keeping Americans safe and keeping America strong."
"This treaty will not diminish anyone's freedom. In fact, the treaty recognizes the freedom of both individuals and states to obtain, possess, and use arms for legitimate purposes."
While 91 countries have signed the treaty, it will not take effect until 50 have ratified it. Only four had done so as of Wednesday.
The Senate's opposition to the treaty poses a significant hurdle for US ratification.
"President Obama demonstrated strong and conscientious leadership by signing the treaty, and it is now time for the US Senate to do its part and ratify the Arms Trade Treaty," said Raymond C. Offenheiser, president of Oxfam America.
"Millions of men, women and children have suffered from armed violence around the world, violence that continues today in Syria, the Democratic Republic of the Congo, Mali and many other countries,” said Offenheiser. “Over the long-term, the Arms Trade Treaty will change how countries engage in the arms trade by requiring exporters to take human rights seriously."
The treaty was put into place earlier this year by the United Nations to regulate trade in tanks, armored combat vehicles, combat aircrafts, attack helicopters, warships, missiles and small arms. It was only adopted after years of work and tough negotiations at the UN to craft it.
"The treaty builds on decades of cooperative efforts to stem the international, illegal, and illicit trade in conventional weapons that benefits terrorists and rogue agents," a senior State Department official said.
It "will help reduce the risk that international transfers of conventional arms will be used to carry out the world's worst crimes."
The Arms Trade Treaty is the first major arms accord since the Comprehensive Nuclear Test Ban Treaty in 1966 and covers all conventional weapons.
Its possible impact on the global arms trade, which is estimated at between $60 billion and $85 billion annually, is not yet known. It will depend on which countries ratify the treaty and how diligently it is upheld once it comes into force.