Aid groups were in talks Tuesday to evacuate 400 people, many starving, from a besieged Syrian town where the UN said suffering was the worst seen in the nearly five-year-old war.
More than two dozen people have reportedly starved to death in Madaya, crippled by a six-month government siege that has made even bread and water hard to find.
On Monday, the first trucks of aid in about four months entered the town, delivering desperately needed food and medicine.
But hundreds of residents remain in need of urgent care, and humanitarian organisations were working on their evacuation, according to International Committee of the Red Cross spokesman Pawel Krzysiek.
"It's a very complicated process that needs permission to realise this humanitarian operation. We are in negotiations with all parties," Krzysiek told AFP.
He said the ICRC, the United Nations and the Syrian Arab Red Crescent were all "working on" the evacuation process.
UN aid chief Stephen O'Brien on Monday called for Syria's government to allow the 400 people to leave the town to receive medical care.
"They are in grave peril of losing their lives," O'Brien told reporters after a UN Security Council meeting.
Permission for safe access must come from "all the parties who govern any of the routes that need to be deployed, either for the ambulances or for any kind of air rescue," said O'Brien.
- 'No comparison' -
The level of suffering in Madaya has no precedent in Syria's war, the UN refugee agency's representative in Syria said.
"There is no comparison in what we saw in Madaya," Sajjad Malik told journalists in Geneva, when asked to compare the devastation in the town to other areas in Syria.
He had travelled to Madaya on Monday along with the UN's aid convoy, and expressed shock at the devastation in the town.
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"There are people in Madaya, but no life. What we saw in Madaya should not happen in this century," Malik said. "We want to make sure the siege is lifted and this is not a one-off."
Syria's envoy to the UN dismissed reports of civilians dying of hunger as fabricated, insisting that the Syrian government "is not and will not exert any policy of starvation on its own people".
Ambassador Bashar Jaafari said the reports were aimed at "demonising" the regime of President Bashar al-Assad.
Madaya is part of a six-month UN-brokered truce reached in September that also includes the nearby rebel-held town of Zabadani, and Fuaa and Kafraya, two government-controlled towns in Syria's northwest.
The agreement foresaw an end to hostilities in the four towns in exchange for humanitarian aid and some evacuations.
A UN official said "one or two more aid deliveries" to the towns would be carried out in the coming days.
Similar local ceasefires have been reached elsewhere in Syria, and typically require rebels to lay down their weapons in exchange for allowing in assistance to inhabitants living under siege.
Doctors Without Borders (MSF) welcomed the calls for the evacuation of hundreds from Madaya but said a long-term solution was needed.
"The medics in Madaya are not equipped for technical hospitalisation of really critical cases," it said in an emailed statement.
Therefore, it was necessary to evacuate "critically malnourished and sick patients" from the town.
But "MSF wants to know what will happen next week, or next month, for critically ill patients."
"Will they have a medical evacuation option? A one-off humanitarian visit and then a return to siege-starvation will not be acceptable," the statement said.
Elsewhere in Syria, government troops backed by pro-regime forces on Tuesday advanced into the main rebel bastion in the northwest province of Latakia, the coastal heartland of Assad's clan.
The push into Salma, which has been held by rebel groups for more than three years, was reported by both the Syrian Observatory for Human Rights monitor and state news agency SANA.
Rami Abdel Rahman, head of the British-based monitor, said pro-government forces were locked in fierce fighting with rebels including Islamist hardliners Ahrar al-Sham and Al-Qaeda-affiliated Al-Nusra Front.