DAMASCUS, Syria — Syrian rebels shelled government-held districts in the northern city of Aleppo on Saturday, killing at least 12 civilians, including three children, state media reported.

Syrian state TV said the shelling, which killed eight members of the same family, also left 45 people injured. The state news agency, quoting an unnamed police official said three children were among those killed. The official said the shells hit a residential area, damaging homes, shops and cars.

The Britain-based Syrian Observatory for Human Rights said rebel attacks in government-controlled areas killed at least five people, including one in an overnight attack. The Observatory, which relies on a network of activists inside the country, said the death toll is likely to rise because many of the injured were in critical condition.

The discrepancy in casualty estimates couldn't be immediately reconciled but such differences are not uncommon in the immediate aftermath of attacks.

Aleppo, once Syria's commercial hub, became a key front in the country's civil war after rebels launched an offensive there in July 2012. The city has since been carved up into areas controlled by the government and others controlled by an array of rebel groups.

Long a stronghold for Syrian rebels, the area, a strategic stretch because of its proximity to the Turkish border, has been a flashpoint since the Islamic State group advanced into the region several months ago.

Syrian rebels have shelled residential areas in government-held parts of the contested city in the past, killing hundreds of people. Government warplanes have dropped explosives-filled barrels on rebel-held neighborhoods in Aleppo and other cities, killing thousands.

On Thursday, Syrian state media said "terrorists" shelled a district in the government-controlled part of the city, killing at least seven civilians.