Regime air raids using barrel bombs on rebel-controlled areas of Syria’s second city of Aleppo at the weekend have killed at least 76 people, including 28 children, activists say.

The number of people “killed after the bombing of areas in the city of Aleppo with explosive-packed barrels (on Sunday) rose to 76”, including “28 children and four women”, said the Syrian Observatory for Human Rights on Monday.

The Observatory said that one youth and 43 men had also been killed in the bombings, but did not specify whether any opposition fighters were among the casualties.

A previous toll from the Observatory – which relies on a network of activists, lawyers and medics for its information – had put the number of killed at 36, among them 15 children.

The Aleppo Media Centre, a network of activists on the ground, called the raids on the northern city “unprecedented”.

The Local Coordination Committees, a network of pro-opposition activists, said military aircraft had dropped barrels packed with explosives on rebel-held areas of Aleppo.

Observatory director Rami Abdel Rahman said the raids had targeted the Sakhur, Ard al-Hamra and Haydariyeh areas of the capital.

Activists posted footage online from the aftermath of the raids in Aleppo, showing bulldozers clearing rubble from the streets as men searched for survivors in bombed-out buildings.

The bombardment came a day after the Syrian Red Crescent delivered food and medicine to Aleppo central prison, which has been under rebel siege for eight months.

Earlier this week, the government announced an amnesty on humanitarian grounds for scores of prisoners held on criminal charges.

More than 126,000 people have been killed in Syria since March 2011, and millions more have fled their homes.