The Syrian Observatory for Human Rights (SOHR) said Syrian forces had seized the southwestern Sheikh Said district from rebels early on December 12, RFE/RL wrote.
SOHR head Rami Abdel Rahman said the Syrian Army is now in "full control" of the important district and holds some 90 percent of the parts of the city once held by the opposition fighters.
Read alsoSyria, Russia pound rebel-held Aleppo but advances halt – ReutersAleppo has been divided since 2012 between government forces in the west and rebel groups who held the eastern part.
An offensive by Syrian forces on the ground aided by Syrian and Russian air attacks has led to the opposition forces losing nearly all of their hold on the city in the past month
Air strikes were continuing to land in eastern Aleppo on December 12, in attacks that have killed hundreds of civilians and drawn condemnation from the international community.
Meanwhile, 200 kilometers to the southeast of Aleppo, IS forces have retaken Palmyra after Syrian troops abandoned their positions in the city.
Syrian officials said they had evacuated some 80 percent of the citizens of Palmyra ahead of the withdrawal. Syrian forces had liberated Palmyra from IS militants in March.
At least 250,000 people have been killed and millions of others displaced since the Syrian civil war began in March 2011.