Up to 20,000 Syrians were stranded on the Turkish border on Friday after fleeing a major Russian-backed regime offensive near Aleppo, where a new humanitarian disaster appeared to be unfolding.
Tens of thousands of civilians have joined an exodus to escape fierce fighting involving government forces who severed the rebels' main supply route into Syria's second city.
On Friday, clashes between the two sides in and around Ratyan, a town near Aleppo, cost 120 lives, said Britain-based monitor the Syrian Observatory for Human Rights.
The UN's Office for the Coordination of Humanitarian Affairs (OCHA) said it estimated "up to 20,000 people have gathered at the Bab Al Salama border crossing and another 5,000 to 10,000 people have been displaced to Azaz city" nearby.
Western nations have accused the Syrian government of sabotaging peace talks that collapsed this week with its military offensive, and Washington has demanded Moscow halt its campaign in support of Syrian President Bashar Al Assad.
US Secretary of State John Kerry on Friday told reporters Russia had said it was prepared to stop the bombings, which he blamed for killing women and children "in large numbers".
"Russia has indicated to me very directly they are prepared to do a ceasefire," he said, adding that another key Assad ally, Iran, had also pledged to support a halt to the violence.
"We will have a much better sense in the next few days of how serious each party is."
The UN Security Council met earlier in the day to discuss the faltering peace process, as Nato head Jens Stoltenberg warned Russian air strikes were "undermining the efforts to find a political solution" -- a charge dismissed by Moscow.
'Rebels on the retreat'
The Observatory estimates 40,000 people have fled the regime offensive near Aleppo.
"Thousands of people, mainly families with women and children, are waiting to enter Turkey," director Rami Abdel Rahman told AFP.
OCHA spokeswoman Linda Tom said another 10,000 people were thought to have been displaced to the Kurdish town of Afrin, elsewhere in northern Aleppo.
"The fighting has also disrupted major aid and supply routes from the Turkish border," she said.
Aleppo province is one of the main strongholds of Syria's opposition, which is facing possibly its worst moment since the country's brutal conflict began in 2011.