Senior international envoys began gathering in New York on Thursday to seek UN backing for an ambitious US and Russian plan to seek a negotiated ceasefire in Syria's brutal civil war.
US Secretary of State John Kerry has already travelled to Moscow this week to assure Bashar al-Assad's key Russian ally that Washington is not seeking "regime change" in Syria.
On Thursday, he was to meet Saudi Foreign Minister Adel al-Jubeir in New York to reassure Assad's most implacable foe that the United States is not going soft on the Syrian strongman.
Kerry's high-stakes diplomatic balancing act aims to keep both Moscow and Riyadh on board as the 17-nation International Syrian Support Group (ISSG) battles to cobble together peace talks.
Washington and UN Syrian envoy Staffan de Mistura want Assad's regime and the armed opposition groups ranged against him to send delegates to peace talks some time on or after January 1.
If a ceasefire can be reached in Syria's four-and-a-half-year-old civil war, then Syrian troops, Russia and a US-led coalition can focus their fire on the hardline jihadist Islamic State group.
Under a deal struck last month in Vienna, government and rebel negotiators would have six months to form a transitional government and 18 months to organize national elections.
But several question marks still hang over the process.
Will Assad and his foreign backers Russia and Iran agree to sit down with rebel groups they routinely denounce as "terrorists"?
And, will the rebels and their foreign backers countenance talks with a regime that has slaughtered thousands of its own citizens in torture cells or with barrel bombs and poison gas?
On Friday, international envoys -- and Russia's Foreign Minister Sergei Lavrov in particular -- want to hear from Saudi Arabia how its efforts to mediate a rebel coalition are progressing.
And US State Department spokesman John Kirby said Jordan would give an update on its role in the process -- drawing up a list of which "terrorist" groups should be blacklisted from talks.
Even if a ceasefire is possible, who would monitor it? And who would lead the fight against the IS group and others, such as Al-Qaeda's Al-Nusra Front, left outside the peace process?
To address these and other questions, the International Syrian Support Group will meet at the invitation of the US on Friday morning at a New York hotel to try to narrow their disagreements.
Then, later in the day, diplomats will travel the short distance to the United Nations to seek -- and in all likelihood obtain -- the approval of the UN Security Council for the process.
"So the big result for the afternoon session is obviously this resolution, and the secretary remains confident that we can get there," Kirby said Thursday.
US diplomats concede that the plan is ambitious and that success is not certain, but they are hopeful that Russia and Saudi Arabia will cajole their rival Syrian allies to the table.
President Vladimir Putin, they reason, will not want to see the Russian forces he sent to Syria to shore up Assad's beleaguered regime bogged down in an indefinite conflict.
Meanwhile, the threat of Islamic State group attacks and waves of Syrian war refugees spilling out from Syria into the Middle East and Europe has concentrated minds in other foreign capitals.
But the United States appears to have already made its own compromises in the search for peace.
Where once it shunned Russia and imposed sanctions on its economy to punish Putin for his aggression against Ukraine, now Kerry publicly thanks Moscow for its "constructive" role in Syria.
And -- while the State Department insists there is no change in its policy that Assad has lost all legitimacy to lead Syria -- Washington has noticeably toned down calls for him to step down.
"We emphasized today that the United States and its partners are not seeking regime change, as it is known, in Syria," Kerry said on Tuesday at the Kremlin after talks with Putin.
"What we have said is that we don't believe that Assad himself has the ability to lead the future Syria," he said.
"But we focused today not on our differences... we focused on the political process whereby Syrians will be making decisions about the future of Syria," he said.
It was only after Tuesday's talks with Kerry that Russia -- which had previously been cautious about convening another meeting of the Syrian Support Group -- agreed to take part.
More than 250,000 people have died since Syria's conflict erupted in March 2011, and millions more have fled their homes.