Syrian forces and their allies are pushing forwards in a major ground offensive to recapture Aleppo's rebel-held east, as international outrage grows over the fierce bombardment on the city's besieged areas.
Dozens of Russian and Syrian government air strikes continued pounding the devastated city overnight, targeting battlefronts and residential neighbourhoods, according to activists. At least six people were killed in the raids on Sunday morning, activists told Al Jazeera.
The ferocious air campaign "helped regime forces to advance in the north of the city", where they reached the outskirts of the al-Heluk district, Rami Abdel Rahman, director of the Syrian Observatory for Human Rights (SOHR) monitoring group, told AFP news agency.
If pro-government fighters seize Heluk, Bustan al-Basha and, Sakhur - all rebel-controlled neighbourhoods in Aleppo city's north - they will confine opposition factions to a small section in the southeast.
"The air strikes are continuing but now the government and its allies - men from Iraq, Iran, Lebanon - are pushing into the rebel enclave in the east of Aleppo," said Al Jazeera's Zeina Khodr, reporting from the Turkish city of Gaziantep near the Syria-Turkey border.
"They are making progress and they are taking ground from the opposition, particularly in the north of the city."
Later on Sunday, the Syrian army said in a statement carried by state media that rebel fighters should vacate the eastern quarters of the northern city of Aleppo and said it would guarantee them safe passage and necessary aid.
"The army high command calls all armed fighters in the eastern neighbourhood of Aleppo to leave these neighbourhoods and let civilian residents live their normal lives," the statement carried by state news agency SANA said.
"The Russian and Syrian military leaderships will guarantee safe passage for the fighters and will give them aid as necessary."
'The worst we've endured'
Hundreds of civilians have been killed or injured in air strikes since the collapse of the latest ceasefire and the Syrian government's announcement last week of a ground offensive to retake the area.
Helped by their Russian ally, the pro-government forces have gained ground in the area, but the rebels say they have been able to repel some assaults.
Since fighting first broke out there in 2012, Aleppo has been divided by a frontline between rebel forces in the east and government troops in the west.
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An estimated 270,000 people, including 100,000 children, are trapped in Aleppo's eastern districts, which civil defence workers say have been hit by 1,900 bombs in the past week.
"This has been the worst we have endured since the start of the revolution. They are using new weapons, they are using phosphorous bombs, but God willing they won't be able to capture Aleppo," said Mohammed Jadhan, a resident of east Aleppo.
The UN is warning of a humanitarian catastrophe inside the besieged city, where food and medical supplies are running low and people are living in dire conditions.
"Children need milk," resident Omar Madani said. "We can handle hunger, but the children can't."
The military campaign by Syrian President Bashar al-Assad in Aleppo has sparked international condemnation after a series of air strikes on civilian infrastructure, including on the largest hospital in the city's east.
At least two barrel bombs hit the M10 hospital on Saturday, according to the Syrian American Medical Society, which supports the facility, in an attack fiercely condemned by Ban Ki-moon, the UN secretary-general, as a "war crime".
Stephen O'Brien, the UN aid chief also criticised the raid and called on Sunday for immediate action to end the "living hell" of civilians in Aleppo's east.
"The health care system in eastern Aleppo is all but obliterated. Medical facilities are being hit one by one," O'Brien wrote.
He said the latest indiscriminate bombings subjected eastern Aleppo's residents to "a level of savagery that no human should have to endure".
"The clock is ticking. Stop the carnage now," O'Brien added.
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But "apart from issuing appeals, warnings, and condemnations, the international organisation has admitted that there is little else it can do", Al Jazeera's Khodr said.
The Syrian civil war started as a largely unarmed uprising against Assad in March 2011, but quickly escalated into a full-blown conflict.
Five years on, more than 400,000 Syrians are estimated to have been killed, and almost 11 million Syrians - half the country's prewar population - have been displaced from their homes.
Diplomatic efforts to put an end to the war have all but collapsed.
Russia and the US brokered a ceasefire deal in early September, hoping it could open a path to peace, but the truce fell apart a week later.
Relations between the two countries have since been strained amid deepening disagreements.
Russia has said it will press on with its bombing, while the US is threatening to end talks and pursue other alternatives.
For Aleppo's besieged residents, time is not on their side.
"You are always looking at the skies, monitoring the planes," said Abdel Rahman al-Mareih, a resident of east Aleppo.
"Y ou could be alive now, but in five minutes you could easily become a martyr."
Source: Al Jazeera News And News Agencies