Thousands of Syrians were stuck on the Turkish border Friday after fleeing a major regime offensive backed by Russia near Aleppo where a new humanitarian disaster appeared to be unfolding.
Tens of thousands of civilians are reported to have joined the exodus after fierce fighting by advancing government forces who severed the rebels' main supply route into Syria's second city.
Western nations have accused the Syrian government of sabotaging peace talks with its military offensive, and Washington has demanded Moscow halt its campaign in support of President Bashar al-Assad.
The UN Security Council was due to meet later Friday to discuss the faltering peace process, as NATO head Jens Stoltenberg warned Russian air strikes were "undermining the efforts to find a political solution".
The Syrian Observatory for Human Rights, a British-based monitor that relies on a network of sources on the ground, estimates that 40,000 people have fled the regime offensive near Aleppo.
"Thousands of people, mainly families with women and children, are waiting to enter Turkey," Observatory director Rami Abdel Rahman told AFP.
Aleppo province is one of the main strongholds of Syria's armed opposition, which is facing possibly its worst moment since the beginning of the war in 2011.
"The regime is beginning to reap the rewards of the Russian campaign and its advance in Aleppo is all the more important because it suffered setback after setback in the past two years," Abdel Rahman said.
Turkish Prime Minister Ahmet Davutoglu said Thursday that up to 70,000 people were heading to his country, with 10,000 already waiting at the border.
His country already hosts about 2.5 million Syrian refugees.
The Turkish border crossing of Oncupinar near Kilis, which faces the Syrian frontier post of Bab al-Salama north of Aleppo, was closed on Friday morning, and there was no sign of any refugee outflow, an AFP journalist saw.
Footage released Thursday by activists showed hundreds of people, including many children, heading towards the Turkish border, some carrying their belongings in plastic bags on their backs.
"We were driven from our homes because of Russia, Iran, Bashar and (Lebanese Shiite militia) Hezbollah," a child said in the video. "We ask (Turkish President Recep Tayyip) Erdogan to let us into his territory."
More than 260,000 people have died in Syria's conflict and more than half the population has been displaced.
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 been on the offensive since staunch government ally Russia began an aerial campaign in support of regime forces on September 30.
Since then, the regime has recaptured several key rebel towns in Latakia province -- Assad's coastal heartland -- and advanced in Aleppo province and in Daraa in the south.
On Friday the army seized the town of Ratyan, north of Aleppo, with support from dozens of Russian air strikes.
Pro-government troops backed by Russian warplanes also retook a rebel bastion in Daraa used as a launch pad for attacks on the provincial capital, the Observatory said.
Top diplomats from countries involved in trying to resolve the conflict are set to meet again on February 11, but tensions between them remain.
Moscow on Thursday accused Ankara, a key backer of Assad's opponents, of actively preparing to invade Syria, saying it had spotted troops and military equipment on the border.
It came just hours after Davutoglu accused Assad's supporters of "committing the same war crimes" as the regime.
Meanwhile Saudi Arabia said it was ready to join any ground operation in the US-led coalition against ISIS in Syria.
"If there is any willingness in the coalition to go in the ground operation, we will contribute positively in that," Brigadier General Ahmed al-Assiri told AFP.
The UN Security Council was scheduled to meet on Friday for consultations with UN envoy Staffan de Mistura who suspended floundering negotiations in Switzerland on Wednesday until February 25.
On Thursday, US Secretary of State John Kerry said he had warned Moscow to stop targeting the Syrian opposition in what he described as a "robust" phone call with Russian Foreign Minister Sergei Lavrov.