UN Undersecretary General for Humanitarian Affairs Valerie Amos said Tuesday 11 million vulnerable people inside Syria needed urgent humanitarian assistance, of them 6.4 million were internally displaced.
Briefing the UN Security Council on Syria, Amos said many people have been displaced several times.
"Basic assistance to some 4.7 million people who have been hard to reach for months, some for years, continues to be a major challenge," she said.
Further 241,000 people are deliberately besieged, mostly by Government forces, and are denied assistance, Amos confirmed.
She stressed that intense fighting and shifting conflict lines continued to make the delivery of aid difficult and dangerous. "The parties to the conflict continue to put obstacles in the way of the sustained access that humanitarian organizations require," she added.
In Deir Az-Zor and Raqqa, Amos noted that nearly 600,000 people could not be reached by the World Food Program last month due to ongoing violence and the presence of armed groups.
"It is the third month in a row that WFP could not reach people in need in Deir Az-Zor," she said.
Parties to the conflict also continue to block aid deliveries to areas outside of their control, this includes armed opposition groups in Aleppo governorate, who have prevented aid from being delivered to areas under the control of the Islamic State in Iraq and Levant (ISIL), amos told the Council.
The government also continued to use administrative procedures to hinder the rapid and sustained delivery of aid, she complained.
Despite the dangers, the UN and partners were able to reach millions of people in need; "last month WFP and partners delivered food for more than 4.1 million people, 16.5 million people were provided with access to clean water by UNICEF and partners, and over 400,000 people received core relief items," she said.
The support of Turkish and Jordanian governments and the implementation of UN resolution 2165 have helped the UN to deliver food for 144,500 people, health support for 151,000, and other basic assistance for 315,000 people through additional cross-border operations, complementing the work of NGOs that have been operating across-borders not controlled by the Syrian Government for many years.
Despite the modest progress, Amos urged on all parties to ensure that they respect and implement UN resolutions 2139 and 2165.
Without additional funds, the WFP will be forced to end its operations completely within two months, she concluded.
The UNSC session then turned behind closed-doors.
Syrian representative to the UN Bashar Jaafari, speaking to journalists after Amos gave her briefing, criticized Amos for failing to shed on what he called as "scandal of poisonous vaccines" that were smuggled by "terrorist groups" and consequently led to the death of dozens of innocent Syrian children.