A week into the latest round of fighting for the city, the regime controls around a third of the district, the Observatory said.
Both Damascus and its ally Moscow have strongly denied any illegal military use of the chemical.
The renewed bloodshed has stoked global concern, though there has been little sign so far of a plan to halt it.
He urged the worldwide community to "stop averting its gaze" from the "terrible reality" of the conflict. Konashenkov said that United Nations assurances should also include free access to humanitarian caravans for the population, as well as the evacuation of wounded and sick people.
On Wednesday, UN Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator Stephen O'Brien said that between 200,000 and 300,000 civilians were still held by terrorists in the eastern neighborhoods of Aleppo.
The truce deal would have allowed the opposition administration in east Aleppo to remain in place, at least temporarily, in return for extremist fighters leaving. But the government rejected it, insisting the state had to retake control as any alternative would "reward terrorists". This news story is related to Print/167286-Aleppo-civilians-try-to-flee-as-Syria-army-advances/ - breaking news, latest news, pakistan ne.