Around 400 people should be urgently evacuated from the besieged Syrian town of Madaya to receive medical treatment, UN diplomats have said.
Around 35,000 people are trapped in the town and had not received supplies since October until a an aid convoy arrived on Monday.
The UN said that four children were among between 15 and 20 people believed to have starved to death under sieges staged by militants in Syria.
It warned that conditions were sharply deteriorating for some 200,000 within besieged areas such as the town of Madaya.
UN officials added that they had unverified reports of deaths within the city of Deir Al-Zor, where civilians have been cut off by Islamic State fighters.
The western part of the city has been under siege since last March. There has been no electricity for more than 10 months and water is only available for three hours a week, the UN report said.
Emergency food aid has been delivered to some areas such as Madaya in recent days, but many more are still cut off by militants.
At least 50 trucks are taking food and medical supplies to 35,000 people trapped in Madaya which had been cut off from help for months.
An aid convoy intended for starving locals in a besieged Syrian village is due to set off on Monday, amid calls for the world to do more.
Shocking images from Syria shine a light on a cruel, medieval form of torture being inflicted on citizens - starvation, writes Rageh Omaar.