According to the Syrian Observatory for Human Rights, rebels hold about 60% of Aleppo, including key districts such as Bustan al-Qasr and Hanano. The Observatory's director, Rami Abdel Rahman, said the rebels had "almost cut off" government forces in the city center.
"The rebels are now in a very strong position," Rahman told AFP. "They have been able to push back the regime forces and take control of large parts of the city."
The Syrian government has denied the reports of rebel gains, claiming that its forces are still in "firm control" of Aleppo.
"The terrorists are trying to create a false sense of victory," said Syrian Information Minister Omran al-Zoubi. "They will not succeed. The Syrian army will continue to fight until it has liberated every inch of our land."
The fighting in Aleppo has caused a severe humanitarian crisis. Hundreds of thousands of people have been displaced from their homes, and there are severe shortages of food, water, and medical care.
"The situation in Aleppo is desperate," said UN humanitarian coordinator for Syria, Yacoub el Hillo. "Civilians are caught in the crossfire, and they are paying the price for this conflict."
The future of Aleppo is uncertain. The rebels appear to have the upper hand, but the government is unlikely to give up without a fight. The fighting is likely to continue for some time, with devastating consequences for the city's residents.
"The situation in Aleppo is very volatile," said Syria analyst Charles Lister. "It is difficult to say what will happen next, but there is no doubt that the rebels have made significant gains."