UN-sponsored peace talks between the Syrian government and opposition are to get under way in Geneva for the first time in nearly a year.
The meeting follows weeks of difficult negotiations in preparation.
Staffan de Mistura, the UN's special Syria envoy, said on Wednesday he was "not expecting a breakthrough".
The opposition is insisting that the fate of President Bashar al-Assad is on the agenda - something the government has refused to discuss.
At least 300,000 people have been killed since the war began in 2011. More than 4.8m have fled the country and a further 6.3m have been displaced inside Syria itself.
While hopes of a breakthrough at the talks are low, much has changed since the last round broke down in April 2016.
The rebels lost their key bastion of East Aleppo to government forces in December and a nationwide ceasefire (barring certain jihadist groups) has been largely holding for the past several weeks.
The ceasefire was orchestrated by Turkey, one of the main backers of the rebels, and Russia, Syria's ally. Both powers have also sponsored recent rounds of talks between the government and rebels in Kazakhstan, aimed at shoring up the truce.Image copyright AFP Image caption More than 300,000 people have been killed in nearly six years of fighting
However the opposition warned earlier this week that an escalation of attacks by pro-government forces on Damascus suburbs held by rebels threatened to derail the Geneva talks.
More than 100,000 civilians live in these areas, where fighting has intensified since Saturday, the UN says,
The two sides remained far apart on key issues in the lead-up to the talks, including over what should even be discussed.
Speaking on Wednesday, Mr de Mistura said the agenda of negotiations would be based on a 2015 Security Council resolution endorsing a peace process, with the following aims:
- Establishing credible, inclusive and non-sectarian governance
- Setting schedule and process for drafting new constitution
- Holding free and fair elections within 18 months pursuant to new constitution administered under UN observation
The resolution called for "formal negotiations on [the] political transition" in Syria - a long-standing framework for peace backed by the UN.
The form of political transition however differs widely between the warring sides. The opposition insists it must include President Assad's departure, while the Syrian government says only elections can decide Mr Assad's future.
The opposition will be represented at the talks by the High Negotiations Committee - an umbrella group of armed and political factions. The government delegation will be led by Syria's UN ambassador, Bashar Jaafari, a veteran of previous rounds of peace talks.
"Am I expecting a breakthrough? No, I am not expecting a breakthrough," Mr de Mistura told reporters on Wednesday, adding that he hoped the meeting could maintain "a very proactive momentum" for further talks.
He also said Russia had asked the Syrian government to halt its aerial bombardment during the talks.
The talks are expected to start with a series of bilateral meetings on Thursday.