Up to 20,000 Syrians were stranded on the Turkish border 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.
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"The trajectory for the rebels is downwards, and the downward slope is increasingly steep," said Emile Hokayem, a senior fellow at the International Institute for Strategic Studies. "The rebels are on the retreat everywhere."
Turkish Prime Minister Ahmet Davutoglu said Thursday up to 70,000 people were heading to his country, which already hosts about 2.5 million Syrian refugees.
Early Friday, the main border crossing in northern Aleppo was closed and quiet on the Turkish side near the town of Kilis, with no sign of arriving refugees.
But footage released Thursday by activists showed hundreds of people, including many children, heading towards the frontier, some carrying their belongings in plastic bags on their backs.
More than 260,000 people have died in Syria's conflict and more than half the population has been displaced.
- 'Empty words' -
Aleppo city, Syria's former economic powerhouse, has been divided between opposition control in the east and regime control in the west since mid-2012.
Syria's army has recaptured several key rebel towns in Latakia province and advanced in Aleppo province and in Daraa in the south since Russia began its aerial campaign on September 30.
On Friday, the army seized the village of Mayer, north of Aleppo, and half the town of Ratyan with support from dozens of Russian air strikes.
Pro-government troops backed by Russian warplanes also retook a rebel bastion in Daraa used as to launch attacks on the provincial capital, the monitor said.
"What frustrates the rebels the most is that the countries that claim to be their friends are happy with empty words and sitting on the fence," said activist Maamoun al-Khatib.
"Meanwhile Russia and Iran are occupying and violating Syrian territory."
Top diplomats from countries trying to resolve the conflict are set to meet again on February 11 after UN-brokered peace talks collapsed this week.
In New York, the UN Security Council met for closed-door consultations with envoy Staffan de Mistura, who has suspended the floundering Geneva negotiations until February 25.
But tensions remain, with Moscow accusing key opposition backer Ankara of actively preparing to invade Syria, a claim Turkish President Recep Tayyip Erdogan dismissed as "laughable".