Foreign ministers from the two powers, which support opposite sides in the five-year conflict, were poised to hold a “personal meeting” in the Swiss city to push for a peace agreement, according to the Russian side.
And US Defense Secretary Ash Carter told BBC radio on Thursday there was “quite a long way to go” before a final deal could be struck.
Both sides have agreed that a deal would involve a durable ceasefire, humanitarian access to conflict-wracked areas and a resumption of peace talks.
The Syria war has pitted the old Cold War rivals against each other, with Russia flying a bombing campaign in support of Syrian strongman leader Bashar al-Assad and the United States backing rebel groups fighting to oust him from power.
– 18-month transition –
As diplomatic efforts intensified, fighting in the complex war continued to claim lives, with Turkish shelling over the border into Syria killing six US-backed Kurdish fighters.
Pro-regime forces also overran a strategically important district on the southern outskirts of Aleppo Thursday, rolling back nearly every gain from a major month-long rebel offensive there, said the Syrian Observatory for Human Rights.
The government advance in Ramussa further seals off Aleppo’s opposition-held eastern districts, where regime forces backed by the Russian air force have completely encircled opposition-held neighbourhoods.
And with fierce fighting raging in Aleppo, the world’s chemical weapons watchdog voiced concern on Wednesday over the alleged use of toxic chemicals in the flashpoint city.
More than 70 people were left choking Tuesday after regime helicopters dropped barrel bombs on a rebel-held district, according to a monitoring group.
The opposition hopes new talks would result in an 18-month transition that would see Syria governed by a transitional body made up of opposition figures, current government representatives and members of civil society, according to a 25-page blueprint.
The Syrian war, which began as a pro-democracy revolt in 2011 but morphed into a multi-front conflict after the regime unleashed a crackdown, has killed more than 290,000 people and forced more than half the population to flee their homes.
Turkey’s President Recep Tayyip Erdogan said he had agreed with Obama to do “what is necessary” to drive IS out of Raqa.
The deputy prime minister of Turkey later said that talks were underway between the two countries’ militaries.