With violence still raging in Aleppo, US Secretary of State John Kerry is due to meet Russian Foreign Minister Sergei Lavrov and top diplomats from the UN and regional powers in Lausanne.
But even before the talks began, Lavrov appeared to be dampening down hopes of a breakthrough with Russian news agencies on Friday quoting him as saying he had no "special expectations" for the latest diplomatic effort.
World powers to try again for Syria ceasefire
And a French diplomatic source told AFP: "When you see the results from the previous (truce) efforts, quite frankly I'm a bit sceptical about the next ones."
With no let-up in Syrian President Bashar al-Assad's onslaught on eastern Aleppo, the sides will look at how to revive the short-lived ceasefire.
Moscow and Washington hammered out the agreement before it quickly crumbled amid the ferocious assault on the rebel-held part of the city, backed by Russian air power.
The offensive has sparked accusations of potential war crimes from the West.
Lavrov also insisted on Friday that Russia did not plan to present new initiatives on ways to resolve the conflict.
Instead he said Moscow would call for "concrete steps" to implement earlier UN resolutions and the now defunct US-Russia ceasefire deal.
Kerry and Lavrov will be joined in Lausanne by UN Syria envoy Staffan de Mistura, along with the top diplomats of Turkey, Saudi Arabia and Qatar -- all backers of Syrian opposition forces.
Iran, a key supporter of Assad's regime, has said its Foreign Minister Mohammad Javad Zarif will take part as well.
Kerry is then due to head to London, where he is likely to meet up on Sunday with his counterparts from Britain, France and Germany.
Hopes however are low that the talks will lead to a breakthrough in resolving the five-year conflict that has claimed some 300,000 lives.
Some experts think Russia may be playing for time as it seeks to solidify its positions ahead of the US presidential elections, now only weeks away.
"The Russians are seeking to maximise their advantage before (President Barack) Obama's successor -- probably (Hillary) Clinton -- steps in with a likely firmer approach to Syria," said Karim Bitar, a researcher at the Institute for International and Strategic Affairs think tank in Paris.
In Aleppo, the Syrian Observatory for Human Rights, a British-based monitor, said Russian and Syrian warplanes again pounded opposition-controlled eastern districts on Friday.
The intensified bombardment has put yet more strain on rescue workers and medical staff in the besieged east, home to an estimated 250,000 residents.
Overwhelmed rescue workers combed through the rubble of shattered buildings looking for victims of the bombardment.
Turkey fears Russia-US war over Syria
Assad, meanwhile, buoyed by the gains pro-regime forces have made in Aleppo, said he would use a victory there as a "springboard" to capture other rebel strongholds.
"It's going to be the springboard, as a big city, to move to another areas, to liberate another areas from the terrorists," he said in an interview with Russia's Komsomolskaya Pravda tabloid published Friday.
More than 370 people, including nearly 70 children, have been killed in regime and Russian bombardment of eastern Aleppo since the assault began, according to the Observatory.
Dozens of civilians, including children, have also died in rebel bombardment of regime-controlled western districts, according to the monitor, which compiles its information from sources on the ground.
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