Divisions among Syria's opposition and anger over regime blockades almost sank new peace talks in Geneva before they began, and analysts say prospects of a breakthrough at the negotiations remain slim.
On Friday, after four days of suspense, Syria's main opposition umbrella group finally announced it would send representatives to Geneva.
But formidable obstacles remain, including differences over the fate of President Bashar al-Assad, emboldened by recent territorial gains with support from Russian air strikes.
In a sign of the challenges ahead, the Saudi-backed High Negotiations Committee (HNC) said it was sending a delegation "to participate in discussions with the UN, not for negotiations."
The complexities of the conflict, involving a tangled web of moderate rebels, Islamist fighters, Kurds, jihadists and regime forces backed by Moscow and Iran, pose a huge challenge, experts say.
"There is every reason to be pessimistic, and there is no realistic scenario in which a breakthrough would be reached," said Karim Bitar, an analyst at the Paris-based Institute of International and Strategic Relations.
"For the time being, the disconnect between the Geneva process and the realities on the ground has never been bigger."
The conflict began in March 2011 with anti-government protests and has evolved into a multi-sided war that has killed over 260,000 people and displaced more than half the population.
In recent months, world powers have redoubled diplomatic efforts to solve the crisis, fuelled by fear of the Islamic State group's growing power, as well as the pressure of a wave of refugees fleeing to Europe.
They have pinned their hopes on an ambitious UN-backed plan for negotiations in Geneva, followed by the creation of a transitional government, a new constitution, and elections within 18 months.
But analysts say the atmosphere for these talks is even worse than a last round of failed negotiations in Geneva in 2014.
After a series of setbacks last year, Assad's government has gone on the offensive and scored several victories since its key ally Russia began an aerial campaign on its behalf in late September.
"Assad is feeling stronger and stronger so is being inflexible," said Agnes Levallois, a France-based Middle East analyst.
"If anything, Russia and the regime will feel that they are slowly grinding down the opposition, that the trend from now on will not be unfavourable to them," added Yezid Sayigh of the Carnegie Middle East Centre.
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- Assad's future in question -
At the same time, Western powers have moderated their previous insistence that Assad must step aside immediately amid fears of a power vacuum that could benefit IS and push more refugees towards Europe.
"Authoritarian nationalism is back in fashion," Bitar said.
Syria's opposition has long insisted that Assad can have no role in any political transition and must resign at the beginning of any such process.
But even staunch supporters of the opposition, including Washington and Saudi Arabia, appear to be stepping back from that position, which could prove a major stumbling block for talks.
It is "clear to the US and even to the Saudis" that Assad's departure cannot be guaranteed as a precondition, said Sayigh.
"The real question is whether meaningful powers will go from Assad to a transitional council, including some mechanism that ensures that Assad is unable to run in future presidential elections," he said.
With the opposition HNC saying it will not participate in actual negotiations, it remains unclear what the talks can achieve.
The umbrella group said it would participate in the "political process" in a bid to force the government to implement "international obligations and humanitarian demands".
It had hesitated to attend the talks in part over the UN's failure to enforce a 2015 Security Council resolution that demanded humanitarian access throughout Syria, an end to sieges, and protection of civilians.
Sayigh, however, said any success at Geneva would be contingent on a "back-room process" that would see the US and Russia reach an understanding on a way forward.
Perhaps in an effort to reach such an agreement, US Secretary of State John Kerry engaged in shuttle diplomacy ahead of the talks in an effort to narrow the gap between backers and opponents of Syria's regime.
But Emile Hokayem, a senior fellow at the International Institute for Strategic Studies, said the "dynamics on the ground are even less conducive to good-faith negotiations" than during the last round of peace talks in 2014.
"Notwithstanding the energy, the positive outlook, the conditions aren't there."