The United States and Russia began high-stakes talks on Thursday on Moscow's plan for Syria to surrender its chemical weapons as Damascus formally applied to join a global poison gas ban, but Secretary of State John Kerry underscored that U.S. military force may still be necessary if diplomacy fails.
"This is not a game," Kerry said in an appearance with Russian Foreign Minister Sergei Lavrov after opening talks in Geneva aimed at fleshing out Russia's plan to secure and dispose of Syria's stockpiles of chemical arms.
The talks were part of a diplomatic push that prompted President Barack Obama to put on hold plans for U.S. air strikes in response to a chemical weapons attack on civilians near Damascus on August 21.
(Read more: More 'innocent victims' if US strikes Syria: Putin)
The United States and its allies say Syrian President Bashar al-Assad's forces carried out the attack with sarin nerve gas, killing more than 1,400 people, including 400 children. Russia and Assad blame rebel forces.
The United Nations said it received a document from Syria on joining the global anti-chemical weapons treaty, a move Assad promised as part of a deal to avoid U.S. air strikes.
The move would end Syria's status as one of only seven nations outside the 1997 international convention that outlaws stockpiling chemical weapons. Other holdouts include neighbors Egypt and Israel, as well as North Korea.
The United States immediately warned Syria against stalling tactics to avoid military strikes. Assad told Russian state television in an interview broadcast on Thursday he would finalise plans to abandon his chemical arsenal only when the United States stops threatening to attack him.
Kerry expressed some optimism about the talks in Geneva - expected to last two days - saying, "We do believe there is a way to get this done" and that the United States was "grateful" for ideas put forward by Russia to resolve the crisis.
But he and Lavrov differed sharply on U.S. military threats.
"We proceed from the fact that the solution of this problem will make unnecessary any strike on the Syrian Arab Republic," Lavrov said during the appearance with Kerry.