The last remaining food rations are being distributed in besieged rebel-held eastern districts of the Syrian city of Aleppo, the UN has said.
Humanitarian adviser Jan Egeland warned that without a resupply there would be no food left to hand out next week to the 275,000 people living there.
Mr Egeland ruled out airdrops of food, explaining that they were not possible in densely-populated urban areas.
Humanitarian agencies have been unable to get into rebel-held Aleppo since the government siege resumed in September, and the last time significant aid supplies were delivered was in July. The area is under siege by government forces with help from Russian air power.
Government forces launched a major assault on eastern Aleppo in September.
Since then, troops have pushed into several outlying areas with the help of Iranian-backed Shia militias and Russian air strikes.
On October 28, an alliance of opposition fighters, including Islamist militants, started a major offensive to break the government siege, which has been in place on eastern Aleppo since July. But their progress slowed after early gains.
The UN says weeks of air strikes and shelling have killed more than 700 civilians in the east, while rocket-fire has left scores dead in the government-controlled west.
“It is a horrendous situation,” said Egeland, the United Nations’ top envoy on humanitarian efforts in Syria.
The Norwegian diplomat said the UN appealed again last week to the conflict parties to let food, medicine and health workers into eastern Aleppo, and to allow the evacuation of some 300 patients along with their families.
Russian Deputy Prime Minister Sergei Ryabkov said Thursday that Russia is continuing its humanitarian pause of air attacks on eastern Aleppo, in comments carried by the Interfax news agency.
However, Egeland noted that continuing heavy fighting on the ground has made aid efforts impossible.
In addition, the warring sides have raised various conditions that have further complicated UN efforts.
“I haven’t seen a place where there has been so much politicization, manipulation of aid as we have seen in Syria,” he said at a press briefing.
Egeland urged the United States, which backs Syrian anti-government rebels, and Russia to use their influence to unblock the humanitarian operation.
“Parties that are sponsoring the parties on the ground have to help us more,” he said, adding that he was optimistic that a solution would be found.
In the divided city of Aleppo, regime forces made more advances Thursday into areas which were taken by opposition rebels last month, the Britain-based Syrian Observatory for Human Rights said.
The monitoring group said regime troops and their allies managed to take over the Dahiyat al-Assad region west of the city.