"We have been mobilizing, stockpiling, readying ourselves for this great opportunity to deliver this very urgent aid but we need that peace to be reinstated," UN humanitarian office (OCHA) spokesman Jens Laerke told reporters.
A truce brokered by the United States and Russia last week appeared to be holding on its first full day Tuesday.
A key test of the deal will be whether warring parties allow relief to reach people in Syria's besieged areas.
Laerke said the UN was taking time to assess the truce's durability before it deployed aid to hotspots like east Aleppo, AFP reported.
Since the deal was reached on Friday, "there has been a lot of mobilization, frantic activity to be able to rush in aid... as soon as it is safe to do so, however, up to this moment, no, the convoys have not been rolling," Laerke said.
"We need to enter into an environment where we are not in mortal danger."
The UN got the Syrian government’s approval on September 6 to deliver aid to nearly one million people this month, including to the rebel held eastern part of Aleppo, which has been encircled by government forces.
Syria's second city has been a key battleground for weeks.
East Aleppo would initially be supplied with food in trucks coming across the Turkish border if security is guaranteed, OCHA said.