Vienna - The UN will make a fresh push from Thursday to jump-start Syrian peace talks, as violence continues to rage in a seven-year-old war that has killed more than 340,000 people.
The two days in negotiations in Vienna come after eight previous rounds in Geneva, the last one in December, that failed to get the different parties even to talk to each other.
They stumbled over the fate of Syrian President Bashar al-Assad, who has taken the upper hand in the conflict since Russia began backing him militarily in 2015.
Representatives from Assad's government have refused to meet the opposition directly until they drop demands that he leave office.
The UN special envoy, Staffan de Mistura, said on Wednesday that the negotiations in Vienna involving "full delegations" of the opposition and government come at a "very, very critical moment".
Nasr al-Hariri from the main opposition group, the Syrian Negotiations Commission (SNC), said that the next two days would be "a real test for all the sides".
French Foreign Minister Jean-Yves Le Drian said meanwhile in Paris that the talks are the "last hope" for reaching a political solution.
Le Drian also highlighted a "considerable worsening of the humanitarian situation" in Afrin, as well as in Idlib and in Eastern Ghouta.
In the Afrin enclave in northern Syria, Turkey on Saturday launched an offensive with Syrian rebels to oust the Kurdish People's Protection Units (YPG) militia.
"Until the last terrorist is neutralised, this operation will continue," Turkish President Recep Tayyip Erdogan said on Wednesday.
Meanwhile, Russian-backed Syrian troops have been carrying out an offensive since late 2017 in the northwest region of Idlib, the last province still fully outside government control.
This has forced tens of thousands of people to flee. On Sunday the Syrian army said it had captured the vital Abu Duhur military airport.
In Eastern Ghouta, a besieged rebel stronghold outside Damascus, at least 21 people suffered breathing difficulties on Monday, a monitor said, in a suspected chemical weapons attack.
'No interest in compromise'
Russian-backed Syrian forces have also dealt severe blows to the Islamic State group, whose self-proclaimed "caliphate" in Iraq and Syria has largely collapsed.
The Vienna talks come ahead of a "Congress of National Dialogue" peace conference in the Russian Black Sea resort of Sochi backed by Russia, Iran and Turkey on January 30.
The three key regional players have been sponsoring parallel peace talks since the start of last year that have looked to still the fighting.
Sochi is part of a broader Russian push to start hammering out a path to a political solution to end the war, sparking concerns that the Kremlin is looking to sideline the UN.
The focus in Sochi will be on hammering out a new constitution, according to the opposition, something that the UN's de Mistura also wants discussed in Vienna.
While Assad's government has said it will come to Sochi, the SNC has not yet decided, even after a recent visit to Moscow.
Expert Firas Modad from IHS Markit said that progress in Vienna "seems unlikely", and that Moscow, Tehran and Ankara "are the ones driving the negotiation process".
"Assad is focused on total victory, with no interest in compromise," he told AFP.