Syrian army soldiers moved into the Salaheddine district of Aleppo on Wednesday, pushing rebel fighters back as they attempt to control the north Syrian city.
The intensity of the conflict in Syria's biggest city and elsewhere suggests that Assad remains determined to cling to power, with support from Iran and Russia, despite setbacks such as this week's defection of his newly installed prime minister.
"We have retreated, get out of here," a lone rebel fighter yelled at Reuters journalists as they arrived in Aleppo's Salaheddine district. Nearby checkpoints that had been manned by rebel fighters for the last week had disappeared.
Syrian state television said government forces had pushed into Salaheddine, killing most of the rebels there, and had entered other parts of the city in a fresh offensive.
It said dozens of "terrorists" were killed in the central district of Bab al-Hadeed, close to Aleppo's ancient citadel, and Bab al-Nayrab in the southeast.
The military offensive appeared to be the most significant ground attack in Aleppo since rebels seized an arc of the city stretching from the southeast to the northwest three weeks ago.
Joma Abu Ahmed, an activist with the rebel Free Syrian Army, told Reuters that insurgents had fallen back to the nearby neighbourhood of Saif al-Dawla, which was now under fire from army tanks inside Salaheddine and from combat jets.
Some rebels denied retreating and an opposition watchdog, the Syrian Observatory for Human Rights, said fighting in the area was the most violent since insurgents first moved in.
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