Over 40 people were killed in continuous rebel shelling of a Kurdish-dominated district in the city of Aleppo on Saturday, a Russian monitoring base said.The shelling, mainly by the Al-Qaeda-linked Nusra Front, targeted the district of Sheikh Maksud, a predominantly-Kurdish district, controlled by the Kurdish People's Protection Units, Xinhua reported.The incessant shelling injured 100 people, an escalation deemed as a breach of the recently established and shaky truce, said the report.Meanwhile, 11 people including a child were killed in shelling of government-controlled areas in Aleppo, namely Masharqa, Midan and al-Faid.The Syrian Observatory for Human Right said Saturday's shelling was intense.The US-backed Syrian Democratic Forces rebels are still trying to advance toward the city of Manbej, controlled by the Islamic State group, in Aleppo.The Syrian army is also engaged in battles against the Nusra Front and like-minded groups, mainly near the town of Khan Tuman.Aleppo, Syria's second largest city and once an economic hub, is significant due to its location near the Turkish border.Each party in the conflict is now fighting to consolidate its position and claim more territory in that key area.