Representatives of more than 60 countries lined up at U.N. headquarters in New York to sign the first international treaty to regulate the $70 billion global conventional arms trade.
Argentina was the first to sign the Arms Trade Treaty the General Assembly approved in April. Iran, Syria and North Korea cast the only votes against the treaty.
But the United States was not among the countries signing on Monday.
A statement from U.S. Secretary of State John Kerry said the world's top arms exporter will sign as soon as the official U.N. translations of the treaty are completed. The statement said the treaty is "an important contribution to efforts to stem the illicit trade in conventional weapons, which fuels conflict, empowers violent extremists, and contributes to violations of human rights."
The National Rifle Association, a powerful U.S. pro-gun lobbying group, opposes the treaty and has vowed to fight its ratification by the U.S. Senate when it reaches Washington.
The U.N. Treaty sets standards for cross-border transfers of conventional weapons ranging from small arms to tanks and attack helicopters. It would also create binding requirements for states to review cross-border arms contracts to ensure that weapons will not be used in human-rights abuses, terrorism, violations of humanitarian law or organized crime.
Russia, China, India and 20 other countries abstained from the April 2 vote. Many nations that abstained criticized the treaty as discriminatory. U.N. diplomats say that the treaty's effectiveness could be limited if major arms exporters and importers refused to sign it.
The treaty will enter into force 90 days after 50 nations have ratified it.