"We have been mobilising, 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 today.
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.
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"We need to enter into an environment where we are not in mortal danger."
The UN got the regime'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's estimated 250,000 people have not received aid since early July, when regime forces cut off the last supply route.
The other towns covered in the September 6 agreement are Moadamiyat al-Sham Madaya, Zabadani, Foua and Kefraya.