Beleaguered rebels in northern Syria faced double defeat on Monday by both the Russian-backed regime and advancing Kurdish militia, as tens of thousands of displaced amassed on the Turkish border.
The worsening refugee crisis has pushed Germany and Turkey to ask NATO for help policing Turkey's shores, after two dozen more migrants drowned there en route to Greece.
In Ankara, German Chancellor Angela Merkel held talks with Turkish leaders, saying the two countries would ask a meeting of NATO defence ministers whether and how NATO could support coastguards.
Merkel said she was "horrified" by the suffering of people stranded on the Syrian-Turkish border after fleeing fighting in northern Syria.
Fierce clashes in the north of Aleppo province -- sparked by a week-long government assault with Russian air support -- have displaced tens of thousands of people.
The United Nations estimated that 31,000 people have fled from areas near and in Aleppo city, a vast majority of them women and children, said Linda Tom, spokeswoman of the UN's humanitarian aid organisation.
Eight informal camps on the Syrian side of the border are at "full capacity", she said, amid reports that refugees are sleeping rough in fields and on roads.
Government troops and allied forces have seized a string of rebel-held villages, bringing them to about 20 kilometres (12 miles) from the Turkish frontier.
"It's the first time since 2013 that the Syrian regime has been this close to the Turkish border in Aleppo province," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, a British-based monitor.
- Rebels 'collapsing' -
Kurdish forces have also pushed further east from their bastion in Afrin, seizing six villages in recent days after rebel groups withdrew.
Opposition fighters are now squeezed "between the pincers of the army, which is pushing north, Kurdish forces coming from the west, and IS which dominates the east," Abdel Rahman said.
The regime offensive, one of the largest yet in the north, has cut a major rebel supply route out of Aleppo city.
Regime forces now have their sights set on taking Tal Rifaat, one of three remaining rebel bastions north of the provincial capital.
After capturing the village of Kafeen late Sunday, government forces are now just five kilometres (three miles) south of Tal Rifaat.
A rebel spokesman said opposition groups were "collapsing" because regional powers were not shoring them up.
"The difference between them and us, it's that we don't benefit from the help of our allies, while the regime gets all sort of support from its allies," said Haitham Hammo, a spokesman for Jabha Shamiya (Levant Front).
According to analyst Fabrice Balanche, Syria's regime aims to "close off the Turkish border to deprive the rebels of their logistical support".
But "the Syrian army is avoiding street fighting -- it's too hard. It advances in open areas and cuts off communication lines held by rebels, who then fall apart," Balanche told AFP.
- 'Total impunity' of regime -
More than 260,000 people have been killed and millions displaced in Syria's bloody war, which diplomatic efforts have so far failed to resolve.
The most recent round of indirect negotiations brokered by the United Nations in Geneva last month was "suspended" until February 25.
Last week, UN Secretary General Ban Ki-moon told The Financial Times newspaper that "aerial bombing continued" when the talks began, making it "extremely difficult" for negotiations to take place.
On Monday, the Russian foreign ministry sharply criticised Ban, saying he had "practically" accused Russia of torpedoing the talks.
"This is clearly not what happened," the ministry said in a statement.
"We have always considered and continue to consider that comments from the chief administrator of an global organisation... should remain impartial and objective," it said.
In a scathing report published on Monday, UN investigators accused the Damascus government of "exterminating" prisoners in regime jails and detention centres.
"The mass scale of deaths of detainees suggests that the government of Syria is responsible for acts that amount to extermination as a crime against humanity," commission head Paulo Pinheiro told reporters in Geneva.
"Nearly every surviving detainee has emerged from custody having suffered unimaginable abuses," Pinheiro said.
Based on 621 interviews -- many of them with former detainees who witnessed deaths while in custody -- the report adds to a huge body of evidence from the commission and others, detailing horrific abuse, torture and killings in Syrian-run jails.
Decrying the atmosphere of "total impunity" reigning in Syria, commission member Carla del Ponte slammed the UN Security Council for "doing nothing".