Written by James Denselow
Parties have yet to agree on a list of opposition groups who may attend, as both sides seek more assurances.
Talks meant to be held in Geneva next week between both sides of Syria's civil war - opposition groups and President Bashar al-Assad's government - are far from certain to take place.
Although the UN special envoy for Syria, Staffan de Mistura, briefed the Security Council in a closed meeting on Monday about these muchanticipated talks, there is still no consensus on who should be invited.
"Obviously we hope that the negotiations will take place but there are some questions which have to be dealt with," French Foreign Minister Laurent Fabius said.
Last month, the Security Council issued a rare, unanimous show of support for negotiations to be held between the Assad government and opposition groups.
But UN Secretary-General Ban Ki-moon is now urging countries supporting opposing sides in the conflict to redouble efforts to agree on a list of opposition groups to be invited to peace talks. Compiling a list has not been an easy task, especially when regional rivals Iran and Saudi Arabia accuse each other of supporting "terrorists" in Syria.
Russian President Vladimir Putin also made it clear during talks with Qatar's EmirTamim bin Hamad Al Thani in Moscow that he believes the list for the opposition delegation drawn up in Saudi Arabia should include more secular figures and Kurdish representatives.
But even opposition groups set to be invited have not committed to participating in the Geneva talks.
They accuse the Assad government of not genuinely seeking a political solution, citing previous Geneva talks as being deliberately obstructive and derailed by his representatives.
"It's thought this time around, the format to begin with will be days of proximity talks," Al Jazeera's Diplomatic Editor James Bays reported. "The two sides will be kept in separate rooms - with Mr De Mistura shuttling between them."
Source: James Bays, Aljazeera
The death of Syrian Islamist leader, Zahran Alloush on December 25 is a reminder that the Syrian regime is willing to risk the Vienna process in order to further its own more direct interests.
The peace plan and its constitutional milestones towards a better Syria are both ambitious and fragile: the plan has succeeded in crystallising parts of the Syrian opposition in Riyadh earlier in December and set in motion direct talks in the new year, making a rare optimism for 2016 to be the year in which the conflict goes in a better direction.
However, the killing of Alloush has already put a halt to the evacuation of opposition elements from the much beleaguered Yarmouk refugee camp and led other opposition leaders to question the regime's intentions towards the "peace" process.
Yet we should not forget that the Vienna process did not come about because of the desire of the regime. Indeed, the initial talks that set out the course ahead did not feature Syrian actors, but instead had patrons and allies from all sides around the table.
In contrast to the earlier Geneva process it appeared that in Vienna, global powers were serious enough about building a peace process that couldn't be hijacked by the main fighting protagonists themselves.
With the targeting of Alloush, it would appear likely that the Syrian regime is trying to restore its own agency in the shadow of a Vienna process by which it feels marginalised. This is a period of huge danger and opportunity for the range of actors that make up the Syrian opposition. They face being labelled as "extremist" and excluded from the nascent peace process or being acknowledged as "moderate" legitimate players and then assassinated. As Human Rights Watch's director Ken Roth tweeted, Alloush's killing "is part of Assad's strategy of trying to reduce [the] choice to him or ISIL".
The importance of this moment is matched by the need for leadership among the opposition to ensure not only the right agreements within the Vienna process, but also to bring about legitimate implementation of any deal. Leaders are important, and nowhere more so than in set peace conferences. Without these figures, we may be left with a shell of a process - all political theory but no actors left to carry it out.
Bearing this importance in mind, the tactics of "decapitation" or targeting of an enemy's leadership are not new or original.
In December last year opposition groups in East Ghouta accused the regime of waging a campaign of targeted assassination against its leaders. Throughout the conflict numerous car bombs have killed opposition leaders without clarity over who was directly behind the attacks. The Assad regime famously has links to the assassination of former Lebanese Prime Minister Rafik Hariri and other "anti-Syrian" politicians in the country. It may be nominally happy to "talk" to the opposition, but we should be under no illusions that they would happier see them dead.
More dangerous for the fragile, ambitious but desperately needed process is if the Russians are found to be involved in the killing either directly (they carried out the air strike) or indirectly (it was their intelligence that led to Alloush's killing).
The National Coalition of Syrian Revolution and Opposition Forces has already accused the Russians of conducting these killings. It is one thing for the Syrians - the object of the Vienna process - to try to assert independence from the process, it's quite another for the Russians - co-creators of the Vienna process - to be seen to be taking out significant opposition leaders weeks before talks are scheduled to start.
The Russians may claim that until there is full agreement on who the "legitimate" opposition are, all anti-Assad groups remain potential targets.
There is strong onus on the other key players in the Vienna process, particularly the United States and the European Union, to get clarity on what happened to Alloush, guarantees from the Russians about their intentions and guarantees towards the actors who will make up a key part of a process that they have co-designed. Meanwhile, the more marginalised the regime feels, the more desperate its actions are likely to become, and nobody can be surprised by its simultaneously satisfying the diplomatic obligations expected of them by their Russian allies and doing their upmost to kill opposition leaders on the ground.
(James Denselow is a writer on Middle East politics and security issues and a research associate at the Foreign Policy Centre.)