US Secretary of State John Kerry on Sunday spearheads a bid to drag Syria's opposition forces into peace talks with President Bashar al-Assad's regime.
At a Paris meeting that represents a critical juncture for international efforts to end a bloody conflict that has claimed more than 130,000 lives, Kerry and ministers from 10 other countries in the "Friends of Syria" grouping will seek to persuade the opposition National Coalition to attend talks due to start later this month in Switzerland.
The Coalition is profoundly divided over the issue: its main component, the Syrian National Council has long maintained that it will not enter peace talks without clear assurances that Assad will have no role in the transitional government the talks will aim to establish.
At talks in Istanbul last week, the different factions were unable to agree on terms for their attendance at the so-called Geneva II talks that are scheduled to get under way in Montreux on January 22.
Coalition leader Ahmad Jarba will be in Paris on Sunday and senior diplomats at the US State Department and in France have voiced cautious optimism that he will bow to intense pressure to ensure the rebels hold what would be the first direct talks with Assad's regime since the conflict erupted in March 2011.
"There are people all around the world doing their best to get them there and get them there with a unified position," said a senior US official involved in preparing the talks.
He described himself as "reasonably confident" that the opposition will accept that joining peace talks is the best option they have against a background of military stalemate and mounting combat fatigue in the nearly three-year-old civil war.
"I think in the final analysis they won't want to miss that opportunity, because frankly there's no other game, really," the official, speaking on condition of anonymity, told reporters.
A French diplomat added: "We think it is important that they decide to attend, even if it is only to show that you have an opposition willing to agree a process of transition on one side and, on the other, a regime that might be willing to put people on the plane to Geneva but not to negotiate a political solution."
Officials acknowledge however that advances by Syrian forces in recent days have made it harder for the opposition to contemplate sitting down with representatives of the Assad regime.
Government troops on Saturday seized a previously rebel-held town in the north of the country and pushed toward part of Aleppo, the main city in northern Syria.
Observers of the conflict believe the government advances are due to opposition forces having become preoccupied with fighting a jihadist group, the Islamic State of Iraq and the Levant, with which they were previously allied.
Clashes between the mainstream opposition and ISIL loyalists have left an estimated 500 people dead in the last week.
The ISIL, which has been accused of terrorising areas it controls, currently occupies a number of frontline positions in the Aleppo area and has threatened to abandon them.
Hopes of progress towards peace in Syria rose last year when Assad agreed to give up the regime's chemical weapons after the West pulled back from the brink of threatened military intervention.
Opposition leaders fear that deal, which involved Syria's ally Russia becoming a pivotal player in the efforts to end the conflict, has conferred a new legitimacy on the regime at a time when misgivings about the influence of radical Islamist groups like ISIL have increased in the West.
Monzer Makhous, the National Coalition's ambassador in France, told AFP that Assad should be required to suspend the use of heavy weapons and agree to the opening of humanitarian corridors as a condition of talks starting.
Sunday's talks will also focus on whether Iran, which has been instrumental in propping up the Assad regime, should be invited to the Geneva II talks.
US officials continue to maintain the idea is a non-starter but Russia has been lobbying hard for Tehran to be brought into the process and the issue is likely to dominate discussions on Monday between Kerry, his Russian counterpart Sergei Lavrov and Lakhdar Brahimi, the UN-Arab League special envoy to Syria.
As well as the the United States and hosts France, the countries taking part in Sunday's meeting are Britain, Egypt, Germany, Italy, Jordan, Qatar, Turkey, Saudi Arabia and the United Arab Emirates.