Number of besieged areas in Syria rises to 18
Speaking at the UN Security Council, the UN's humanitarian chief, Stephen O'Brien, and the head of the World Food Programme, Ertharin Cousin, called on the Syrian regime to allow sustained access to besieged areas and to the estimated 4.5 million people in hard-to-reach areas.
Officials said the rare convoys that reached a few besieged communities such as Madaya and Zabadani earlier this month, after images of emaciated Syrian children were widely shared online, are not enough and that the food delivered will soon run out.
"One-off access ... is not the kind of access we need to prevent starvation," UN humanitarian chief Stephen O'Brien told reporters.
He also called for immediate medical evacuations from besieged areas for the sick and wounded.
O'Brien called the idea of airdropping aid to besieged areas "risky" and insufficient, but diplomats said all options are still being discussed.
"Some simply say to me: 'the UN should break the sieges' - but that would be reckless. It would entail sending convoy drivers and humanitarian workers into the line of fire," O'Brien added.
|Some simply say to me: 'the UN should break the sieges' - but that would be reckless. It would entail sending convoy drivers and humanitarian workers into the line of fire
- Stephen O'Brien, UN
WFP chief Ertharin Cousin told reporters that for airdrops to happen, her agency would need secure airspace, assurances that the aid gets to the most vulnerable and enough space on the ground to safely drop the "large tonnages" necessary to be meaningful food aid.
The UN says food aid reached less than one percent of people in besieged areas last year.
Cousin said it is "just a matter of time" before the world again sees the kind of images of suffering Syrians that promoted international outrage and the rare aid convoys earlier this month.
While the UN says all sides in the conflict have blocked the delivery of aid, it has repeatedly criticised Syria's government.
The UN secretary-general's latest report on the crisis says that since the beginning of 2015, just 13 inter-agency convoys have been approved by the government and completed, out of 113 requested.
"We cannot for one minute think the situation is improving," the US ambassador to the UN, Samantha Power, told reporters.
The Syrian regime and members of the opposition are due to hold UN-brokered talks in Geneva on Friday, however the opposition has demanded the regime end its sieges and stop indiscriminate airstrikes before negotiations can take place.
Agencies contributed to this report.