Syrian forces have retaken the largest rebel-controlled area in east Aleppo.
The capture of Hanano district, in north-east Aleppo, gives the army an advantage in its drive to seize other opposition-held areas, activists say.
Hundreds of civilians have reportedly fled into Hanano.
Some 275,000 people are under siege as the army’s offensive – now in its 13th day – continues. The assault has killed 219 civilians, the UK-based Syrian Observatory for Human Rights says.
Among the victims were 27 children, the monitoring group added. Reports suggest there is a lack of medical supplies and food.
Capturing all of Aleppo would be a major victory for Syrian President Bashar al-Assad after six and a half years of conflict.
Hanano was the first neighbourhood in Aleppo taken by rebels in 2012.
Syrian forces regained the district on Saturday – a move making it easier for them to isolate the northern districts of east Aleppo from the southern ones.
Air strikes launched as part of the recent government offensive were described by activists as the most intense ever, leaving the streets deserted.
More than 400 civilians fled overnight to Hanano and were taken to regime-controlled areas, the Observatory said.
Meanwhile the rebels intensified rocket attacks on the government-controlled western districts of Aleppo. Their attacks have killed 27 civilians since the offensive began, the Observatory said, including 11 children.
Aleppo, once Syria’s commercial and industrial hub, has been divided roughly in two since 2012, with the government controlling the west and rebels the east.
In the past year, Syrian troops have broken the deadlock with the help of Iranian-backed militias and Russian air strikes.
Russia says its air force is active in other parts of the country, but not operating over Aleppo.