Aid convoys are due to be sent to Syria's besieged areas, UN envoy Staffan de Mistura has said.
He said it would be a test of whether warring parties were committed to allowing in humanitarian supplies.
Among the areas due to receive aid is the town of Madaya, where people have been dying of starvation.
World powers last week agreed to seek a nationwide "cessation of hostilities" and to accelerate and expand aid deliveries.
