GENEVA — A diplomatic breakthrough Saturday on securing and destroying Syria’s chemical weapons stockpile averted the threat of U.S. military action for the moment and could swing momentum toward ending a horrific civil war.


Marathon negotiations between U.S. and Russian diplomats at a Geneva hotel produced a sweeping agreement that will require one of the most ambitious arms-control efforts in history.


The deal involves making an inventory and seizing all components of Syria’s chemical weapons program and imposing penalties if President Bashar Assad’s government fails to comply will the terms.


After days of intense day-and-night negotiations between U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov and their teams, the two powers announced they had a framework for ridding the world of Syria’s chemicals weapons.


The U.S. said Assad used them in an Aug. 21 attack on the outskirts of Damascus, the capital, killing more than 1,400 civilians. That prompted President Barack Obama to ready American airstrikes on his order – until he decided last weekend to ask for authorization from the U.S. Congress. Then came the Russian proposal, and Obama asked Congress, already largely opposed to military intervention, to delay a vote.


Kerry and Lavrov said they agreed on the size of the chemical weapons inventory, and on a speedy timetable and measures for Assad to do away with the toxic agents.


But Syria, a Moscow ally, kept silent on the development, while Obama made clear that “if diplomacy fails, the United States remains prepared to act.”


The deal offers the potential for reviving international peace talks to end a civil war that has claimed more than 100,000 lives and sent 2 million refugees fleeing for safety, and now threatens the stability of the entire Mideast.


Kerry and Lavrov, along with the U.N.-Arab League envoy to Syria, Lakhdar Brahimi, said the chances for a follow-up peace conference in Geneva to the one held in June 2012 would depend largely on the weapons deal.


The U.S. and Russia are giving Syria just one week, until Sept. 21, to submit “a comprehensive listing, including names, types and quantities of its chemical weapons agents, types of munitions, and location and form of storage, production, and research and development facilities.”