The Syrian government has agreed to allow emergency UN aid into three besieged towns – including the rebel held town of Madaya, close to Damascus – where it is reported people are staving to death.
Entry to Madaya and nearby Zabadani is strictly controlled by pro-Assad forces.
The rebel encircled towns of Foah and Kefreya are also due to receive assistance.
The last delivery humanitarian aid arrived in Madaya last October, but has since been a no-go area, despite numerous requests from the UN for access.
Around 40,000 people are believed to be cut off.
As snow falls, the situation is becoming ever more desperate.
Reports suggest that those who try to leave the town in search of food run the gauntlet of snipers and landmines.
The UN says it will deliver aid in the coming days.