Helicopters could be used to deliver aid to besieged areas of Syria, the UN has said, on the eve of an emergency meeting of the Security Council about the issue.
Humanitarian access in Syria has been a key sticking point in stalled UN-backed peace talks aimed at ending the five-year war that has killed at least 280,000 people and displaced millions.
United Nations spokesman Stephane Dujarric yesterday said helicopters would have to be used to carry aid to 15 of 19 besieged areas that include densely populated towns.
"In urban areas, airdrops are not feasible, so you are talking about the use of helicopters," he said.
"One can imagine the security challenges for that -- plus the security challenges of flying helicopters over the skies of Syria."
The comments came as a US-backed alliance of Kurds and Arabs pressed its advance in northern Syria towards the town of Manbij, held by the Islamic State jihadist group.
The US-led coalition also dropped ammunition to Syrian rebels fighting IS as they try to prevent the jihadists from entering the town of Marea, a monitoring group and US defence official said.
In Syria's second city, Aleppo, 23 civilians were killed by regime bombardments, the civil defence said, while a suicide bombing near a mosque killed at least two in the government coastal stronghold of Latakia.
The Security Council is due to meet on Friday to discuss the UN plan for airdrops.
Last month the United Nations said that if it did not see improvement on aid access to besieged areas by June 1, it would task its food agency to carry out drops.
A deputy to the UN special envoy to Syria Staffan de Mistura said "as long as the World Food Programme has not yet finalised its plans, I don't think there's something imminent".
Ramzi Ezzedine Ramzi said airdrops were "very complex" and would need Damascus' approval.
On Wednesday, land deliveries reached two towns besieged by government forces where civilians are facing severe food shortages.
A truce allowed a convoy to enter Daraya near Damascus for the first time since late 2012, while another entered nearby Moadamiyeh for the first time since March.
