Rebel fighters have vowed to make Aleppo the "grave" of President Bashar al Assad's regime as they hang on in Syria's second city in the face of overwhelming firepower.
Areas held by the Free Syrian Army were shelled and strafed by helicopter gunships as government troops sought to crush the opposition in the country's commercial hub.
The military claimed it had retaken control of the Salaheddine district, which straddles a route that could be used by troop reinforcements from the south, after heavy fighting.
But rebel fighters, patrolling the city in flat-bed lorries flying the green, white and black flag of the uprising, said they were holding on to the area despite the pounding it was taking.
Mohammed, a young fighter, told Reuters: "We always knew the regime's grave would be Aleppo.
"Damascus is the capital, but here we have a fourth of the country's population and the entire force of its economy. Bashar's forces will be buried here."
Colonel Abdel Jabbar al Oqaidi, head of the Free Syrian Army military council for Aleppo, insisted that the rebels still controlled "between 35 and 40% of Aleppo".
About 200,000 residents have fled the violence in the last two days, according to the UN, but many remain trapped in the city.
An activist working with a network of Aleppo volunteers organising food and shelter told AFP that as many as 70,000 people were currently being sheltered in schools, university dorms and charity centres.
He said that In the makeshift shelters "there is no problem between the supporters of the government and the opposition. They are all in the same position".
Others had been displaced had left the under-fire neighbourhoods and were staying with friends and family elsewhere in the city.
UN Secretary General Ban Ki-Moon said he was "deeply concerned" about the situation in Aleppo.
"I am extremely concerned by the impact of shelling and use of other heavy weapons on civilians in Aleppo and other locations in Syria," he said.
"I remind the parties in the conflict of their obligations under the international humanitarian law and human rights laws and urge them to exercise restraint and avoid any further bloodshed."