Hopes are building for a Syria peace conference next month backed by Washington and Moscow, but serious obstacles -- not least deep divisions within the opposition -- could still scupper the talks.
And experts say that even if the negotiations, tentatively scheduled for mid-June in Geneva, do go ahead, few expect a breakthrough in resolving an escalating conflict that has already claimed more than 94,000 lives.
"The conference will possibly take place, but whether it will have any impact is another question," said Christopher Phillips, a lecturer on the Middle East at the University of London.
"It's unlikely that this can work. But for now it is the best hope," he said.
Russia and the United States have been pushing hard for the regime and opposition to come together for the talks -- dubbed "Geneva 2" because they aim to build on a peace initiative held in the Swiss city in June last year.
The talks last year brought together top diplomats from the five permanent members of the UN Security Council -- the United States, China, Russia, France and Britain -- and representatives of Turkey, the Arab League and the European Union.
US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov met in Paris on Monday for private discussions on moving the process forward, with Lavrov admitting afterwards that organising the new conference was "a very tall order".
Diplomatic sources say organisers are struggling to agree on the basic principles of the talks, in particular whether the departure of President Bashar al-Assad should be a precondition.
The opposition has also balked at some of the representatives put forward by Damascus, in particular Prime Minister Wael al-Halqi, but experts say this is unlikely to hold up the negotiations.
Iran's participation is another sticking point. The United States and France are opposed to Tehran taking part, but Russia said Tuesday that the participation of Assad's other main international ally was "key" for Moscow.
"Iran without question is one of the most important nations," Lavrov said.
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But the main obstacle remains the opposition's failure to agree on whether to participate, let alone on who would attend the talks.
"The biggest problem is on the rebel side with finding someone to represent them," Phillips said. "Finding people that everyone can agree on will be difficult."
Opposition talks on choosing a new leadership and on attending the conference have dragged on for days in Istanbul, highlighting the deep-rooted differences among Assad's opponents.
Russian Deputy Foreign Minister Sergei Ryabkov said Tuesday that the lack of leadership among the Syrian opposition was the "main obstacle" to holding the peace conference.
Russia on Tuesday also accused the European Union of damaging peace efforts by agreeing to lift an arms embargo on Syria's rebels, saying the move would "directly harm" work to organise the conference.
Analysts said the lifting of the embargo -- pushed mainly by Britain and France -- may have been aimed at giving an incentive to the opposition to take part in the talks.
A final decision on delivering arms has not yet been made and could be conditional on the opposition joining the peace efforts.
Still, few are holding out hope of the talks having a significant impact.
"I'm very sceptical about them. I don't see that they're going to make much of a difference," said Salman Shaikh of the Brookings Doha Center.
"The situation on the ground is an escalating conflict and that is the real dynamic," he said.
Assad's forces have taken the offensive against rebel fighters in recent weeks, including with an attack on the opposition stronghold of Qusayr backed by a key regime ally, the Lebanese Shiite movement Hezbollah.
Fears of a spillover from the conflict have also been growing, with three Lebanese soldiers killed near the border on Tuesday.
Shaikh said it was more likely to be military action, not diplomatic manoeuvring, that would prove decisive in the coming months.
"The regime has a feeling that it is on the offensive, it is trying to gain an irresistible momentum," he said. "The next three months are going to be absolutely crucial."