Syrian rebels have gained ground in government-held western Aleppo, seizing an army barracks in one district, but have been pushed back elsewhere.
The fighting in the country’s former economic powerhouse is some of the fiercest since the Syrian conflict began in the northern city in mid-2012.
Elsewhere, government forces launched a major operation to recapture Zabadani, the last opposition-held town in the Qalamoun region near Damascus.
The Syrian Observatory for Human Rights reported heavy clashes in several parts of Aleppo’s west side.
It said fighters from the Conquest of Aleppo alliance of mostly moderate forces had on Friday captured a former research centre being used as a military barracks.
“This is a significant strategic step in terms of the battle that has been going on in Aleppo in the past two years,” said Observatory director, Rami Abdel Rahman, adding that it opened up lines of attack against several nearby districts controlled by government forces.
A video online showed the capture, with fighters from one of the groups firing in the air, the three-starred flag of the Syrian uprising behind them.
The Observatory said government forces had tried unsuccessfully to recapture the facility overnight and launched air raids against it on Saturday, prompting the rebels to partially evacuate.
Conquest of Aleppo and a second rebel grouping, Ansar al-Sharia, which is dominated by Islamists and al-Qaida’s local affiliate al-Nusra Front, began operations against government-held districts of Aleppo this week.
The attacks have prompted fierce clashes and heavy bombardments, with rebels firing hundreds of rockets and the government launching dozens of air strikes.
The assault began on Thursday, when Ansar al-Sharia attacked several neighbourhoods including Zahra, where an air force intelligence facility is based.
The coalition initially made progress but was pushed back by government forces on Friday night, the Observatory said. The monitor said government jets carried out some 40 air strikes, and at least 29 Ansar al-Sharia fighters were killed on Friday.
Thomas Pierret, a professor at Edinburgh University and a Syria expert, said the latest fighting could prove significant. The recent rebel progress in and around western Aleppo “is the first real progress by the rebels in Aleppo since ... July 2013”, he said.
Control of the city has been largely divided between the government in the west and rebels in the east since shortly after fighting arrived there in mid-2012. Frontlines have remained fairly static since then, though both sides have at times sought to encircle the other by advancing in the countryside around the city.
But he cautioned it was too early to say whether things might “evolve rapidly”, saying the west would prove to be difficult terrain for rebel forces because its buildings are ideal for regime snipers and its avenues wide enough for government tanks.Pierret said the loss of the Scientific Research Centre meant “the regime has lost an important line of defence, which leaves their control of west Aleppo more vulnerable”.
In the Qalamoun region, government forces backed by Lebanon’s Shia movement, Hezbollah, started a battle to capture the last rebel-held town in the area, which lies north of Damascus on the Lebanese border.
“Army units supported by the Lebanese resistance this morning launched a major operation in the Zabadani region in Damascus province,” Syrian state television announced.
The Observatory confirmed heavy fighting was under way between regime forces and their allies and rebels in the vicinity of Zabadani, which was one of the first towns to fall to the opposition in 2012.
The battle was announced a day after rebels attacked an army outpost at the entrance to the town, which the regime responded to with some 90 air raids using barrel bombs and missiles, the monitor said.
Regime troops backed by Hezbollah have also recaptured most of the Qalamoun region, which was once a bastion of the opposition.
In addition to Zabadani, opposition forces have bases in the mountainous part of Qalamoun that spans the border, but Hezbollah has been gradually advancing in that region in recent weeks.