© Karam Al-Masri/AFP/Getty ImagesA member of the White Helmets stands amid the rubble of a destroyed building after airstrikes in Aleppo in October.
The rescue group said it believed it had less than 48 hours before the Syrian army, backed by Iranian militia, reached the districts in which it has been operating.
"If we are not evacuated, our volunteers face torture and execution in the regime's detention centres," the group said. "We have good reason to fear for our lives."
The plea came as Sergei Lavrov, the Russian foreign minister, said the Syrian army was suspending all military operations in eastern Aleppo to allow as many as 8,000 residents to leave. Russian and US officials would discuss detailed documents at the weekend in Geneva, he said, adding that Moscow was determined to beat all "terrorists" until their full elimination, in line with UN security council resolutions.
Russia has hinted at such deals in the past, only for them to collapse. The US said it welcomed the "indication that something positive could happen but we're going to have to wait and see". White House spokesman Josh Earnest added: "Our approach to the situation has been to listen carefully to what the Russians say, but scrutinise their actions."
The UN security council will be briefed by the UN's special envoy for Syria, Staffan de Mistura, at a closed doors session on Friday.
The White Helmets in Aleppo fear they will be "be treated as terrorists" and could face detention or execution by advancing regime troops. "We hold the ICRC [International Committee of the Red Cross], the United Nations and the [UN] security council responsible for our lives and we call on you to secure safe passage," a statement added.
Western sources said there were credible reports of people being arbitrarily arrested and executed in Aleppo, though there was a lack of firm information.
Comment: If there is a lack of firm information, how "credible" can these mysterious Western sources be??
The White Helmets operate in rebel-held territory throughout Syria and have won international acclaim for their work in the aftermaths of attacks. The Bashar al-Assad regime has always described the group as a western propaganda tool, but it contends it has no political affiliation, working only to save civilian lives in highly dangerous circumstances. It was nominated for the Nobel peace prize this year and is backed by UK funds.
The plea symbolises the collapse of the resistance in eastern Aleppo, with two thirds of the city now captured by the regime, and as few as 100,000 civilians still in rebel held parts of the city. Despite the regime advance, many citizens have not left due to the lack of a safe route and the risk of re-entering the conflict zone.
Comment: The plea symbolises the collapse of Western-backed terrorist propaganda. Note how the Guardian still refers to the legitimate Syrian government which rescues its civilian population as the "regime" while referring to the murderous terrorist groups as "resistance".
Jan Egeland, the UN's humanitarian coordinator for Syria in Geneva, said the parties to the conflict were poles apart on agreeing the terms of a ceasefire.
Five months of negotiations over aid plans had all failed and produced "nothing", Egeland said, adding that it was up to Moscow and Washington to agree a safe voluntary evacuation from east Aleppo.
"The member states that are supposed to help us get access to civilians in the crossfire are poles apart in how they regard what is happening in Syria. We are not having a united humanitarian diplomacy by the parties and we see that in a diminishing access on the ground.
"I have never been in my many, many years of humanitarian negotiations in as difficult negotiations and as frustrating talks that produced nothing in spite of thousands of contacts with all of the parties, and it is with bitterness and frustration that we have to report that we have not been able even to evacuate the wounded."
A rebel call on Wednesday for a five-day ceasefire and the evacuation of civilians to opposition territory was rejected by Assad.
Comment: The same rebels who held the civilians hostage. The Syrian army evacuated the civilians. Facts beat propaganda.
The Russians insisted they were discussing the details of a ceasefire but, in the past few weeks, Russia has repeatedly shown a willingness to negotiate but not reached a deal.
Lavrov spoke to the outgoing US secretary of state, John Kerry, in Hamburg, but the US has virtually no negotiating leverage.
Kerry will confer with foreign ministers in Paris on Saturday to discuss the humanitarian consequences of the crisis in Aleppo, and to map out a political strategy for after the city's likely fall. Many diplomats insist the fall of Aleppo will not mean the end of the civil war, but simply signal the start of a more brutal insurgency phase.
Comment: Western powers do not want peace, they want a continuation of the slaughter via their proxy "moderate" terrorists.
The rebels are likely to want to flee to Idlib, 35 miles west of Aleppo, or to the Euphrates Shield area north of Aleppo.
The capture of eastern Aleppo will put Syria's five major cities, the south, central spine and western flank bordering the Mediterranean, under Assad's control, but power is still fragmented. Assad wants to press ahead to retaking the whole of the country, but is dependent on Russian and Iranian support to do so.
Comment: Learn more about these so-called "do gooder" White Helmets: