The Syrian army has advanced towards the Turkish border in a major offensive backed by Russia and Iran that rebels say now threatens the future of their nearly five-year-old insurrection against Syrian President Bashar al-Assad.
Iranian backed-militias played a key role on the ground as Russian jets intensified what rebels call a scorched earth policy that has allowed the military back into the strategic northern area for the first time in more than two years.
"Our whole existence is now threatened, not just losing more ground," said Abdul Rahim al-Najdawi from Liwa al-Tawheed, an insurgent group.
"They are advancing and we are pulling back because in the face of such heavy aerial bombing we must minimise our losses."
The Syrian military and its allies were almost 5km from the rebel-held town of Tal Rafaat, which has brought them to around 25km from the Turkish border, the rebels, residents and a conflict monitor said.
The assault around the city of Aleppo in northern Syria has prompted tens of thousands to flee towards Turkey, which is already sheltering more than 2.5 million Syrians, the world's largest refugee population.
In the last two days escalating Russian bombardment of towns north west of Aleppo, Anadan and Haritan, brought several thousand more, according to a resident in the town of Azaz.
Rebel-held areas in and around Aleppo are still home to 350,000 people, and aid workers have said they could soon fall to the government. Turkish President Tayyip Erdogan was quoted at the weekend as saying Turkey was under threat.
Damascus says it wants to take back full control of Aleppo, Syria's largest city before the civil war erupted five years ago. It would be a huge strategic prize for Assad's government in a conflict that has killed at least 250,000 people across the country and driven 11 million from their homes.
After around a week of heavy Russian air strikes, Syrian government troops and their allies broke through rebel defences to reach two Shi'ite towns in northern Aleppo province on Wednesday (local time), choking opposition supply lines from Turkey.
The Syrian army's success in opening a route to the Shi'ite towns of Nubul and Zahraa enabled it to cut a main highway that linked rebel held areas in the northern countryside of Aleppo with the eastern part of Aleppo held by insurgents since 2012.
The latest gains by the Syrian government bring it to the closest point to the Turkish border area since August 2013, the Syrian Observatory for Human Rights said.
The prospect of the loss of Azaz, just a few miles from the Bab al Salama border crossing, would virtually wipe out the insurgents from their main stronghold in northwest Syria.