Following days of intense, long negotiations, the United States and Russia have reached an agreement on a framework to secure and destroy Syria's chemical weapons by the mid-2014 and impose U.N. penalties if the Assad government fails to comply.
The deal, announced by U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov in Geneva on Saturday, includes what Kerry called "a shared assessment" of the weapons stockpile, and a timetable and measures for Syrian President Bashar Assad to comply.
It was not immediately clear whether Syria had signed onto the agreement, which requires Damascus to submit a full inventory of its stocks within the next week.
"The world will now expect the Assad regime to live up to its public commitments," Kerry told a packed news conference at the hotel where negotiations were conducted since Thursday night. "There can be no games, no room for avoidance or anything less than full compliance by the Assad regime."
Lavrov added, cautiously, "We understand that the decisions we have reached today are only the beginning of the road."
The negotiations are considered critical to breaking the international stalemate blocking a resumption of peace talks to end the Syrian civil war, now in its third year.
Under the framework agreement, international inspectors are to be on the ground in Syria by November. During that month, they are to complete their initial assessment and all mixing and filling equipment for chemical weapons is to be destroyed.
The deal calls for all components of the chemical weapons program to be removed from the country or destroyed by mid-2014.
"Ensuring that a dictator's wanton use of chemical weapons never again comes to pass, we believe is worth pursuing and achieving," Kerry said.
Noncompliance by the Assad government or any other party would be referred to the 15-nation U.N. Security Council by the Organization for the Prohibition of Chemical Weapons. That group oversees the Chemical Weapons Convention, which Syria this week agreed to join.
The U.S. and Russia will press for a Security Council resolution enshrining the chemical weapons agreement under Chapter 7 of the U.N. Charter, which can authorize both the use of force and nonmilitary measures.
But Russia, which already has rejected three resolutions on Syria, would be sure to veto military action, and U.S. officials said they did not contemplate seeking such an authorization.
The U.S. and Russia are two of the five permanent Security Council members with a veto. The others are Britain, China, and France.
Still, U.S. officials stressed that President Barack Obama retains the right to launch military strikes without U.N. approval to protect American national security interests.
Lavrov indicated there would be limits to using such a resolution.
"Any violations of procedures ... would be looked at by the Security Council and if they are approved, the Security Council would take the required measures, concrete measures," Lavrov said. "Nothing is said about the use of force or about any automatic sanctions."
Kerry made clear that the U.S. believes the threat of force is necessary to back the diplomacy.
"I have no doubt that the combination of the threat of force and the willingness to pursue diplomacy helped to bring us to this moment," Kerry said.
Under the 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 local and form of storage, production, and research and development facilities."
International inspectors, the U.S. and Russia agreed, should be on the ground in Syria by November and complete their initial work by the end of the month. They must be given "immediate and unfettered" access to inspect all sites.
Kerry said the two sides had come to agreement on the exact size of Syria's weapons stockpile, a sticking point.
U.S. officials, speaking on condition of anonymity because they were not authorized to publicly discuss details of the negotiations, said the U.S. and Russia agreed that Syria had roughly 1,000 metric tons of chemical weapons agents and precursors, including blister agents, such as sulfur and mustard gas and nerve agents like sarin.
These officials said the two sides did agree on the number of chemical weapons sites in Syria.
U.S. intelligence believes Syria has about 45 sites associated with chemicals weapons, half of which have "exploitable quantities" of material that could be used in munitions. The Russian estimate is considerably lower; the officials would not say by how much.
U.S. intelligence agencies believe all the stocks remain in government control, the officials said.
U.N. inspectors are preparing to submit their own poison gas report this weekend. Secretary-General Ban Ki-moon said Friday that he expected "an overwhelming report" that chemical weapons were indeed used on the outskirts of Damascus on Aug. 21.
Obama called for a limited military strike against Assad's forces in response, then deferred seeking congressional approval to consider the Russian proposal.
The commander of the Free Syrian Army rebel group, Gen. Salim Idris, told a news conference in Turkey that the Russian initiative was a "waste of time" and that rebels will continue "fighting the regime and work for bringing it down."
He said that if international inspectors come to Syria in order to inspect chemical weapons, "we will facilitate their passages but there will be no cease-fire." The FSA will not block the work of U.N. inspectors, he said, and the "inspectors will not be subjected to rebel fire when they are in regime-controlled areas."
Idris said Kerry told him by telephone that "the alternative of military strikes is still on the table."
Based on reporting by The Associated Press.