The UN yesterday urged Russia to give it control of humanitarian passages out of Aleppo in northern Syria where besieged residents cowered indoors afraid to use what some called "death corridors".
A monitoring group, meanwhile, reported that at least 18 civilians were killed in air strikes in the city of Aleppo and in the provincial town of Atareb.
The Britain-based charity Save the Children said a maternity hospital it supports in northwestern Idlib province was bombed yesterday, killing two people and injuring babies in incubators.
Syrian regime ally Russia has said three humanitarian passages would be opened for civilians and surrendering fighters seeking to exit Aleppo's eastern districts.
Only a dozen of Aleppo residents trickled out through one passage yesterday, while others wanting to flee were turned back by rebels, the Syrian Observatory for Human Rights monitor said.
An AFP correspondent in east Aleppo said streets were empty with residents holed up indoors and shops shuttered.
Ahmad Ramadan from the opposition Syrian National Coalition accused Russia and the regime of forcing civilians to flee through continued bombing raids.
"Aleppo residents are calling the corridors that Russia is talking about 'death corridors'," he said.
The Britain-based Observatory said at least eight civilians were killed in regime air strikes that hit two eastern areas of Aleppo, warning the death toll could rise as more were trapped under the rubble.
It later reported unidentified air strikes on the rebel-held town of Atareb in Aleppo province that killed 10 people and wounded many other seriously, calling the raids a "new massacre".
UN envoy Staffan de Mistura said Russia, which has been carrying out air strikes alongside Syrian regime planes, should let the United Nations take charge of the corridors.
"Our suggestion is to Russia to actually leave the corridors being established at their initiative to us," he said.
"How can you expect people to want to walk through a corridor, thousands of them, while there is shelling, bombing, fighting?"
Russia's deputy defence minister, Anatoly Antonov, said Moscow was prepared "for the closest and most constructive cooperation" with the United Nations and international humanitarian organisations.
But he warned that rebels would not be allowed "to enter the city and fuel the terrorists with weapons and ammunition".
The UN says around 250,000 people have been trapped in Aleppo's eastern districts since July 17 when pro-regime forces surrounded the area.
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.
Aid agencies and analysts said the humanitarian corridors must be used to send desperately needed supplies to those areas which have not received any medical aid since July 7.
"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," said the International Committee of the Red Cross.
The US-based International Rescue Committee warned that those left behind in east Aleppo risked starvation and called for a pause in the fighting.
Analyst Karim Bitar from the French think-tank IRIS said: "Aleppo residents are facing a terrible existential dilemma, they often have to chose between risking starvation or risking to die while fleeing."
Humanitarian effort have often been used during the conflict "as cynical ploy to advance geopolitical interests."
Russian defence minister Sergei Shoigu announced 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".
Analysts said losing Aleppo would be a major blow for the rebels and a possible turning point in Syria's five-year-old conflict.
"In Aleppo, getting civilians to leave would both serve its propaganda and its military objectives," said Emile Hokayem, senior fellow at the International Institute for Strategic Studies.
"The regime uses massive, indiscriminate force to brutalise civilians to force them to kneel or reject the rebel groups," he added.
More than 280,000 people have been killed in Syria's war which erupted in 2011 with a brutal crackdown on anti-government protests before becoming a complex conflict involving many groups, including jihadists.
Save the Children voiced "outrage" over the attack of the maternity hospital it supports in Idlib.
"Several babies were injured when their incubators crashed to the floor, and a woman who was six months pregnant had her leg severed," it said.
The Observatory said a jihadist from Al-Nusra Front, which has changed its name to Jabhat Fateh al-Sham, was killed in the raid in the rebel-held town of Kafar Takharim.
It also reported that IS had executed 24 civilians after seizing a village in northern Syria.