The UN has been unable to make aid deliveries to Syrians for two months, with President Bashar al-Assad withholding approval, a UN adviser said on Thursday.
Aid conveys require authorisation from the regime and security guarantees from armed groups before crossing into besieged areas.
"It's an all-time low in giving us the facilitation letters," Jan Egeland, the UN humanitarian adviser, told reporters in Geneva, according to Reuters.
"When we need their ability to influence the parties the most, in this bleak hour for humanitarian work, humanitarian diplomacy seems to be totally impotent. We're getting nowhere at the moment," she added.
More than 90 percent of Syrians living under siege reside in rebel-held eastern Ghouta.
Two insurgent groups - Jaish al-Islam and Fayaq al-Rahman - control the area, lobbing mortars into Damascus that also kill civilians.
In December, UN Secretary General Antonio Guterres called on the Assad regime to be referred to the International Criminal Court for blocking aid deliveries.
A Russian- and US-chaired UN task force published six months ago a list of 500 people in need of urgent medical care and evacuation from eastern Ghouta.
Damascus has continued to ignore the request.
At least 15 have already died, according to IRIN News.
Assad still withholding aid deliveries, UN official says
Assad still withholding aid deliveries, UN official says
MENA
1 min read
Restrictions on the entry of food, medicine and humanitarian supplies to Syria's eastern Ghouta is a man-made crisis, the UN has said.
Severe suffering is commonplace in Damascus' besieged suburb of eastern Ghouta [AFP]