entrance, in order to assault it. Elite troops are being sent... but so far the army has been unsuccessful," said Syrian Observatory for Human Rights director Rami Abdel Rahman.
"The army's use of surface-to-surface missiles on Aleppo is part of that attempted advance," Abdel Rahman said.
On Friday, at least 29 people, among them children, were killed in three surface-to-surface missile strikes on eastern Aleppo, the Observatory said.
The missiles, which targeted the district of Ard al-Hamra area of Tariq al-Bab, also injured about 150 other people, said the Britain-based Observatory.
Activists said the missiles were launched from Base 155 near Damascus, though their reports could not be verified.
Just four days earlier, 33 people including 15 children were killed in a missile attack on the nearby district of Jabal Badro, said the Observatory.
Activists have reported the army's use of surface-to-surface missiles on various targets in northern Syria since late 2012.
A security official in Damascus said late last year that such missiles were a Syrian-made version of Scuds, while Nato has since reported the use of ballistic missiles in the country.
Elsewhere in Aleppo, shelling on the Maadi district of Aleppo caused a building to collapse, said the Observatory. An unknown number of people were killed there, it added.
In the province, rebels fought troops on Saturday morning near Aleppo international airport and Nayrab air base, southeast of the provincial capital, said the Observatory.
On February 12, rebels announced an assault on several airports -- military and civilian -- in Aleppo province, in a bid to stop warplanes from taking off.
The insurgents have since captured two air bases and a military complex tasked with securing the international airport and nearby Nayrab air base.
Friday's violence left some 110 people dead across Syria, according to a preliminary toll compiled by the Observatory.
Some 70,000 people have been killed in Syria's nearly two-year war, the UN says.