(Adds quotes, background, reaction)
By Paul Eckert and Arshad Mohammed and Louis Charbonneau
UNITED NATIONS, Sept 24 (Reuters) - U.S. Secretary of State John Kerry, in a move that puts the Obama administration at odds with the American gun lobby, will sign the U.N. Arms Trade Treaty regulating the $70 billion international trade in conventional arms, diplomats from two countries said at the United Nations on Tuesday.
The diplomats said Kerry would sign the treaty on Wednesday on the sidelines of the annual U.N. General Assembly in New York.
U.S. President Barack Obama addressed the assembly on its opening morning on Tuesday with a speech that focused on Syria, Iran and other Middle East hot spots.
The treaty, which requires ratification by the U.S. Senate and has been attacked by the America's pro-gun National Rifle Association (NRA), would help Western countries press to curtail Russian arms sales to Syria, whose government has been accused of widespread abuses in a two-year-old civil war.
Amnesty International Secretary General Salil Shetty called Kerry's decision "a milestone towards ending the flow of conventional arms that fuel atrocities and abuse."
The United States and 86 other signatory countries "must implement the Treaty and bring to an end the supply of weapons to countries where they would be used to commit or facilitate genocide, crimes against humanity, war crimes or other serious human rights violations," he said in a statement.
President Goodluck Jonathan of Nigeria, whose country has been repeatedly attacked by a cross-border Islamic jihadist militant group called Boko Haram, told the United Nations such rebellions are "sustained by unfettered access by non-state actors to illicit smart arms and light weapons."
"For us in Africa these are the weapons of mass destruction," he said.
The U.N. General Assembly on April 2 adopted the treaty by a vote of 154 for, including the United States, three against, and 23 abstentions. The no votes were cast by Iran, North Korea and Syria, U.N. records show.
The NRA, which has opposed the treaty from the start, called the April vote a sad day for the United States, the world's No. 1 arms exporter.
Among NRA arguments against the treaty are that it undermines American sovereignty and disregards the Second Amendment of the U.S. Constitution, which guarantees citizens the right to bear arms.
The U.N. Office for Disarmament Affairs has said the treaty would not "interfere with the domestic arms trade and the way a country regulates civilian possession."
"It will prevent human rights abusers and violators of the law of war from being supplied with arms. And it will help keep warlords, pirates, and gangs from acquiring these deadly tools," the U.N. office said on its website.
Frank Januzzi, deputy executive director of Amnesty International USA, called the move "a very significant win for 20 years of human rights activism" by his global organization and by Oxfam International, a confederation of groups focused on poverty and injustice.
Januzzi said the treaty could be applied to the conflict in Syria, making arm sales to the government illegal under international law. Russia, Syria's main arms supplier, and China abstained in the April U.N. vote and have not signed the pact.
"This will increase the pressure on Russia to sign. It will increase the pressure on China as well," he said in a telephone interview. (Reporting by Paul Eckert; Editing by Bill Trott and Xavier Briand)