A new UN report says the delivery of aid to millions inside Syria is becoming even more difficult as the Islamic State group closes down humanitarian efforts and Syria's government puts more obstacles in the way.

The UN secretary-general's latest monthly report says 700,000 people in areas controlled by the Islamic State group again went without food assistance in February after the World Food Program had to halt deliveries. The areas include parts of Aleppo and the group's de facto capital of Raqqa.

At the same time, Ban Ki-moon's report says Syria's government has started asking for lists of beneficiaries before aid can be delivered, and that all communication with government ministries should go through the foreign ministry.

The UN says 12 million people in Syria need aid, and nearly 4 million have fled the country.

The report expresses concern that global attention is focused on the threat of groups like the Islamic State while the Syrian people feel increasingly abandoned.

"Despite the demands of the Security Council to end the conflict, events and attacks that should shock our collective conscience and spur us into action have become a daily occurrence, often without comment or attention being paid to them," Ban's report says.

The UN and others have struggled to deliver aid to those affected by the civil war, a conflict which has entered its fifth year with more than 220,000 killed so far.

The report says more aid has been brought over the border from Syria's neighbours in recent months, with food rations for more than 771,000 people sent between December and February, up from 170,000 between September and November.