Syrian helicopter gunships and artillery pounded two key areas of Aleppo on Tuesday, extending the army's campaign to control the country's biggest city, but rebel fighters said troops loyal to President Bashar al-Assad had been forced to retreat.
Heavy gunfire sounded from the Salaheddine district in the southwest of the city, where rebels 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.
A rebel commander in Aleppo said his fighters' aim was to push towards the city centre, district by district, a goal he believed they could achieve "within days, not weeks".
The rebels now control 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 rebel 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 rebel 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 rag-tag rebels 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 rebels 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 rebel-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 rebel fighters died during clashes with Syrian forces in Salaheddine.
Rebel 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.
Rebels have captured a small number of tanks and armored vehicles but they do not seem to have used them in combat yet.
Against a background of divisions among major powers over Syria, U.S. President Barack Obama and Turkish Prime Minister Tayyip Erdogan discussed in a telephone call how they could work together to speed up political transition in Damascus.
Erdogan, who once enjoyed close ties with Assad, has become one of his fiercest critics and has demanded he step down.
"In the talks, they took up the co-ordination of efforts to accelerate the process of political transition in Syria, including Bashar al-Assad leaving the administration and the meeting of the Syrian people's legitimate demands," Erdogan's office said.
Turkey hosts more than 40,000 Syrian refugees, many of them in border camps where they complain of poor conditions.
Amid growing concern about security on its frontier, Turkey sent at least four heavily armed military convoys to the border with Syria on Monday, although there has been no indication that Turkish forces will cross into its neighbor.
(Additional reporting by Yara Bayoumy in Beirut; Writing by Giles Elgood; Editing by Alistair Lyon)