WASHINGTON - US Secretary of State John Kerry set off to meet his Russian counterpart Wednesday, as moves to eliminate Syria's chemical weapons switched to the diplomatic track.
Kerry's talks in Geneva with Foreign Minister Sergei Lavrov, which officials said could last until Saturday, mark a significant shift in the world's response to the war in Syria.
Just as Kerry was leaving, envoys from the five permanent members of the UN Security Council held a first inconclusive meeting on Russia's plan to secure Syria's banned arms.
US President Barack Obama, who on Tuesday set aside a threatened military strike against Bashar al-Assad's regime, has said Moscow's plan could be a "significant breakthrough."
But before Washington can give its full backing, US officials said, Kerry must meet Lavrov and test how serious Russia - Assad's key ally - is about destroying the arsenal.
Backed by a team of arms experts, Kerry will spend two to three days in Geneva poring over the details of Russia's proposal.
Obama has warned the threat of US military force remains on the table, and if Syria backslides US military would "send a message to Assad that no other nation can deliver."
This week's surprise diplomatic opening came after Kerry, in a seemingly off-the-cuff remark, said Assad could avert US military action if he handed over the weapons.
The opening was speedily embraced by Russia, which has already passed to Washington what the State Department called "ideas" containing "a number of components and details."
"Secretary Kerry and Foreign Minister Lavrov spoke this morning in advance of the meeting in Geneva tomorrow," a senior State Department official told reporters.
"They discussed the outlines of the schedule and their shared objective of having a substantive discussion about the mechanics of identifying, verifying and ultimately destroying Assad's chemical weapons stockpile so they can never be used again."
Kerry, who has been the most vocal advocate for Obama's call for strikes to punish Assad, alleged this week that Damascus has 1,000 metric tonnes of deadly chemical agents, including sulfur, mustard, sarin and VX.
In Geneva, US arms experts will seek to hammer out with the Russians a mechanism by which the weapons could be secured and then destroyed under international supervisions.
Aram Nerguizian, from the Center for Strategic and International Studies, a Washington think tank, said the common methods of getting rid of chemical agents are "incineration and neutralization - often through chemical decomposition."
But he warned that the West - anxious to see Syria's chemical weapons disposed of while deeply reluctant to intervene militarily in a bloody civil war - is playing a dangerous game of "geopolitical chicken."
"Even if it takes time, any UN-backed effort to put Syrian chemical weapons under international safeguards will either positively impact or further complicate Syria's civil war," he wrote.
"Which of those two plays out depends on broad international agreement and real world positive engagement by the Assad regime."
While in Geneva, Kerry will also seek to revitalise political moves to end Syria's civil war, in more than 110,000 people have died since March 2011.
He will meet UN-Arab League envoy Lakhdar Brahimi to discuss UN-backed efforts to bring the Assad regime to the table with the opposition to hammer out both a ceasefire and a political transition, in what has been dubbed the Geneva II conference.
The Syrian opposition has reacted with dismay to the Russian plan, warning that negotiations over chemical weapons will distract from peace efforts and will only deepen the chaos and misery in their country.
Nevertheless, Obama's address on Tuesday appears to have indefinitely delayed US military strikes, and on Wednesday, the UN envoys from Britain, China, France, Russia and the United States met at the United Nations.
"Everyone set out their position but there were no real negotiations," a UN diplomat said after the 45-minute closed-door talks, which were held at Russia's UN mission.
UN Secretary General Ban Ki-moon had said earlier that the failure to halt atrocities in war-torn Syria had stained the reputation of the world body and the Security Council powers.
On Tuesday, France, Britain and the United States had pressed for a Council resolution that would impose tough consequences should Damascus fail to hand over control of its banned chemical weapons.
But Lavrov has said it would be "unacceptable" for the Security Council to pass a text to authorise enforcement action against Syria.
France has indicated it is ready to modify, within limits, its draft resolution but intends to keep the military option on the table as a means of pressuring the regime.
At Russia's urging, Damascus has said it wants to put its arsenal of chemical weapons under international supervision in compliance with the 1993 convention banning the weapons.
China, which traditionally joins Russia in opposing Western military interventions, urged all sides to "grasp this opportunity to solve the Syria problem through diplomatic and political means."
With the risk of an attack having receded, Assad - who celebrated his 48th birthday on Wednesday - was free to pursue his battle with a dismayed rebel coalition.
The regime carried out an air strike on a field hospital in the province of Aleppo, killing at least 11 people, according to the Britain-based Syrian Observatory for Human Rights.
Elsewhere, Sunni hardliners killed at least 20 civilians in the central province of Homs, with fighters from the Qaeda-linked Al-Nusra Front and another rebel group attacking three Alawite villages, the Observatory said.
Assad, a secular leader who has largely protected the rights of minorities, belongs to the heterodox Alawite sect which Sunni hardliners consider un-Islamic.
Sunni Arab monarchies Qatar and Saudi Arabia have funded the rebels, while Shiite theocracy Iran has staunchly backed Assad.
Obama himself had cited the sectarian nature of the conflict in resisting earlier calls from Britain, France and several US lawmakers to intervene in Syria.
But Obama called for a limited strike after US intelligence concluded the regime used sarin gas on August 21 attack on rebel-held suburbs of Damascus, killing more than 1,400 people.