Aid agencies on Friday called on Syria's government to end its encirclement of rebel-held east Aleppo as a handful of civilians managed to use humanitarian corridors to flee the ruined city.
Pro-regime forces have surrounded Aleppo's eastern districts since July 17, leaving an estimated 250,000 trapped without reliable access to food or medical aid.
Russia, a key ally of President Bashar al-Assad, on Thursday announced the opening of humanitarian passages for civilians and surrendering fighters seeking to exit the city's rebel-held eastern neighbourhoods.
The Red Cross welcomed the corridors but said Russia and pro-government forces had an obligation to protect everyone in Aleppo, once Syria's economic hub and a battleground city seen as key in its five-year-old conflict.
"Those who decide, for whatever reason, to stay in Eastern Aleppo must be protected, and all sides must allow humanitarian agencies to reach and assess their well-being and needs," the International Committee of the Red Cross said in a statement.
Residents have reported food shortages and spiralling prices in rebel districts since regime forces cut off the opposition's main supply route into the northern city.
The US-based International Rescue Committee said those left behind in east Aleppo risked starvation and called for a humanitarian pause in fighting.
"The people of Aleppo should not be forced to choose between fleeing their homes and remaining under attack in a besieged area," said IRC's acting Middle East director Zoe Daniels.
Russian Defence Minister Sergei Shoigu said on Thursday that three humanitarian corridors were being opened "to aid civilians held hostage by terrorists and for fighters wishing to lay down their arms".
But only a few Aleppo residents were able to leave eastern neighbourhoods through the passages before rebels prevented them from fleeing, according to the Syrian Observatory for Human Rights.
"Around 12 people managed to use the Bustan al-Qasr corridor before rebel groups reinforced security measures and prevented families from approaching the corridors," Observatory director Rami Abdel Rahman said.
The UN has warned that any corridors must be used voluntarily and protection be guaranteed.
An AFP correspondent in east Aleppo said streets were empty on Friday morning, with residents holed up indoors. Shops were shuttered and generators in several neighbourhoods had stopped after their fuel ran out.
Ahmad Ramadan from the opposition Syrian National Coalition accused Russia and the regime of forcing civilians to flee through continued bombing raids.
"What is happening now is not battles, but the complete and systematic destruction of the city and its residents, whether they are civilians or fighters," he told AFP.
Regime aircraft bombed eastern areas of Aleppo overnight, the Observatory said, without specifying casualties.
Analysts say that losing Aleppo would be a major blow for the armed opposition and could signal a turning point in the conflict, which began in 2011 with the brutal crackdown of anti-government protests.
