Geir Pedersen, the UN special envoy for Syria, said on Monday that no single party would be able to dictate the outcome of talks to draft a new constitution for the war-wracked country.
His comments came as members of a constitutional committee began arriving in Geneva ahead of their inaugural meeting on Wednesday.
The 150-member committee comprises equal numbers of government, opposition and civil society representatives, the names of which took almost a year of negotiations to thrash out, such was the distrust between Syria's rival sides.
Whether they write a new constitution or revise the existing one is entirely their decision to take, said Mr Pedersen. From the 150-member panel, 45 will draft the final document and a three-quarters majority will be needed for it to come into force.
“If you want to find a solution to the Syrian crisis no one side can dictate to the others,” said Mr Pedersen. “Trust needs to start to be built up.”
When the idea of a new constitution was first raised more than two years ago, Syria's opposition insisted that President Bashar Al Assad give up power before they enter talks.
They later dropped that demand and UN Secretary General Antonio Guterres announced the formation of the committee during the opening of the world body's General Assembly last month.
Although fighting continues in parts of Syria a new constitution is seen as the pathway to elections.
There remains no indication that Mr Al Assad will step aside. The United States and other western powers want him to leave office as a condition of the country's eventual re-entry to the international community and reconstruction aid.
Such a deal remains a distant and unlikely prospect. The Assad regime is pursuing a military campaign to reclaim all territory. In the last two weeks government forces have made large gains due to a Turkish-led incursion in north-east Syria made possible by the abrupt withdrawal of American troops.
However, the UN-brokered committee does represent progress as it is the first agreement between the Syrian government and the opposition since the civil war broke out in 2011.
“They will need to discuss and to reach a consensus,” Mr Pedersen said, noting that no deadlines had been set because the more than eight-year war had seen “lots of past deadlines passed”.
“It is impossible to say how long it will take for them to complete their work,” the envoy said, insisting it was a process led by Syrians and not Russia, Iran or Turkey, the three countries with the biggest influence on the ground.
The UN assisted in drawing up the civil society list, which includes Syrians from a range of political, religious, ethnic and geographic backgrounds.
This week's talks will be based on UN Security Council Resolution 2254 which calls for a new constitution, UN-supervised elections, and transparent and accountable governance.
Beyond the politics of Syria lies a refugee crisis, tens of thousands in government custody and disputes over the safety of those citizens who wish to return from abroad.
Lebanon and Turkey host the largest number of refugees but both countries say progress is needed to allow them to leave, a process complicated by fears they will face discrimination and reprisals.
Gebran Bassil, the foreign minister of Lebanon, the population of which has increased by more than one million Syrians, last month accused some refugees of pocketing money under UN programmes. They did so while freely moving between their home country and Lebanon, he said.
And Turkish Foreign Minister Mevlut Cavusoglu said that the Syrian regime's military assault in the north-west province of Idlib meant that another “300,000 civilians are on our doorstep”.