Syrian rebels have seized a strategic military centre in government-held western Aleppo city, as fierce battles rage between opposition and regime forces, a monitor said Saturday.
The Syrian Observatory for Human Rights said a coalition of rebel groups had taken the Scientific Research Centre, which was being used as a military barracks.
Observatory director Rami Abdel Rahman said that opened potential lines of attack against several other government-held neighbourhoods.
The alliance of rebels is one of at least two coalitions of opposition fighters that have begun a major operation against government-held districts in Aleppo in recent days.
The grouping that captured the military barracks includes various largely moderate rebel factions.
A second coalition fighting in western Aleppo calls itself Ansar al-Sharia and includes Al-Qaeda's local affiliate Al-Nusra Front.
Aleppo, once Syria's economic powerhouse, has been divided between the government in the west and rebels in the east since shortly after fighting there began in mid-2012.
A video shared online showed the capture of the Scientific Research Centre, with fighters from one of the groups raising the three-starred flag of the Syrian uprising.
The Observatory said regime war planes had carried out extensive raids against the centre on Saturday morning, prompting the rebels to evacuate parts of it.
The monitor said government forces had tried to recapture the centre overnight without success.
Elsewhere in western Aleppo, clashes continued between rebels from Ansar al-Sharia and loyalists around the Zahra neighbourhood.
The group began an assault against Zahra and several other regime-held districts Thursday night, advancing slightly before being pushed back Friday night, as government planes carried out around 40 air strikes.
The Observatory said at least 29 Ansar al-Sharia fighters were killed Friday, but had no details on deaths among regime forces.
Also Saturday, the Observatory said the number of Al-Nusra Front fighters killed a day earlier in an explosion in a mosque in northwestern Syria had gone up to 31.
An initial toll of 25 had been given for the blast, which hit a mosque during Ramadan prayers in the town of Ariha in Idlib province.
Civilians were among the worshippers, but there was no immediate confirmation of civilian deaths.
The Observatory said the blast appeared to have been caused by an explosive device placed at the mosque.
A coalition including Al-Nusra pushed government forces out of most of Idlib province earlier this year.