Ninety-two civilians were killed and 273 others injured Saturday by Assad regime and Russian airstrikes on residential areas in opposition-held parts of Syria's northwestern city of Aleppo, a civil defense official said.

Speaking to Anadolu Agency, Najib Ansari said the warplanes targeted the districts of Bustan al-Qasr, Mashhad, al-Kallasa, Salihiya, and al-Fardos, Sheikh Haider, Ansar, Bustan al-Basha, Ard al-Hamra, Sohr, Tariq al-Bab, Karam Hamud, Mesir, all of which were currently under siege by the Assad regime.

The casualties include women and children. The death toll is expected to rise further due to the limited capacity to rescue victims trapped under collapsed buildings.

On Friday, 86 people were killed by regime and Russian warplanes.

Aleppo has recently come under intense attacks by regime and Russian forces.United Nations Secretary-General Ban Ki-moon is "appalled by the chilling military escalation" in the Syrian city of Aleppo, his spokesman said on Saturday."Since the announcement two days ago by the Assad regime of an offensive to capture eastern Aleppo, there have been repeated reports of airstrikes involving the use of incendiary weapons and advanced munitions such as bunker buster bombs," U.N. spokesman Stephane Dujarric said in a statement.

Since Sept. 19, when Assad regime declared the end of the week-long cease-fire, at least 359 civilians have been killed and 1,407 injured by Assad regime and Russian airstrikes on Aleppo, according to civil defense officials and medical sources in the city.

The attacks have targeted districts in the eastern part of Aleppo besieged by regime forces.

Syria has been locked in a devastating civil war since 2011, when the Assad regime cracked down on pro-democracy protests-which had erupted as part of the Arab Spring uprisings-with unexpected ferocity.

The Syrian Center for Policy Research, a Beirut-based nongovernmental organization, has put the death toll from the six-year-old conflict at more than 470,000.