Syria has authorised the delivery of medicine to opposition-held areas of Aleppo, the World Health Organization says.
WHO official Elizabeth Hoff said the government had also promised access to the Damascus district of Mouadamiya and to Eastern Ghouta, outside the capital.
She said she hoped deliveries to Aleppo could be made by next week.
A UN envoy recently called for a ceasefire in Aleppo, Syria's second city, to allow for the delivery of aid.
Ms Hoff said the deliveries had been negotiated in "top-level" meetings.
"We have had some constraints in the past with delivering surgical supplies, syringes, but the situation is much better at the moment," she said.
Vaccines will be included in deliveries to Eastern Ghouta, which has been closed for a long time, Ms Hoff added.
The UN estimates that some 4.7 million Syrians are in areas that are hard to reach, with at least 240,000 besieged by either the government or the opposition.
Since the conflict in Syria began in 2011 more than 200,000 people have been killed and more than nine million people have fled their homes.