Heavy gunfire sounded from the Salaheddine district in the southwest of the city, where opposition fighters denied they had been driven out by the army. Attack helicopters turned their machineguns on eastern districts for the first time in the latest fighting.
The army said two days ago it had taken Salaheddine, but Syrian state television said on Tuesday government forces were now pursuing the remnants of a group of “terrorists” there, in an indication that the army did not after all have full control of the area.
An opposition commander in Aleppo said his fighters' aim was to push towards the city center, district by district, a goal he believed they could achieve “within days, not weeks.”
The opposition now controls an arc that covers eastern and southwestern districts.
“The regime has tried for three days to regain Saleheddine, but its attempts have failed and it has suffered heavy losses in human life, weapons and tanks, and it has been forced to withdraw,” said Colonel Abdel-Jabbar al-Oqaidi, head of the Joint Military Council, one of several opposition groups in Aleppo.
It has not been possible to verify independently who controls Salaheddine, a district that lies on a major road that the army could use to bring reinforcements into the city.
Oqaidi told Reuters late on Monday more than 3,000 opposition fighters were in Aleppo, but would not give a precise number.
The battle for Aleppo has become a crucial test for both sides in the 16-month-old rebellion. Neither Assad's forces nor the opposition can afford to lose if they hope to prevail in the wider struggle for Syria.
The fighting has proved costly for the 2.5 million residents of Aleppo, a commercial hub that was slow to join the anti-Assad revolt that has rocked other cities, including the capital, Damascus.
While the opposition forces say they will turn Aleppo into the “grave” of the Assad government, thousands of residents have fled the city and those who remain face shortages of food and fuel and the ever-present risk of injury or death.
“We have hardly any power or water, our wives and kids have left us here to watch the house and have gone somewhere safer. said Jumaa, a 45-year-old construction worker, who complained it was nearly impossible to observe the Muslim fasting month of Ramadan, now in progress.
“I would say 99.9 percent of the people aren't fasting. How can you fast when you hear mortars and artillery hitting the areas nearby and wondering if you will be next?” he said.
Makeshift clinics in opposition-held areas struggle to deal with dozens of casualties after more than a week of fighting.
The opposition Syrian Observatory for Human Rights said more than 100 people, 73 of them civilians, were killed in Syria on Monday. It said five opposition fighters died during clashes with Syrian forces in Salaheddine.
Opposition fighters, patrolling in pick-up trucks flying green-white-and-black “independence” flags, face a daunting task in taking on the well-equipped Syrian army, even if the loyalty of some of its troops is in doubt.
Armed with Kalashnikov assault rifles, machineguns and rocket-propelled grenades they face a military that can deploy fighter jets, helicopter gunships, tanks, armored fighting vehicles, artillery and mortars.
Opposition forces have captured a small number of tanks and armored vehicles but they do not seem to have used them in combat yet.