Bombs drops by the Syrian government helicopters have killed at least 71 people in the northern province of Aleppo.
The Syrian Observatory for Human Rights said "at least 71 civilians were killed, and dozens were wounded, when regime helicopters dropped barrel bombs on the city of Al-Bab and in Al-Shaar in east Aleppo city".
Al-Bab lies about 40km (25 miles) northeast of Aleppo city and is controlled by the extremist Islamic State (Isis) group. IS also confirmed the attack in a statement posted on Twitter.
An AFP correspondent at the scene reported seeing the bodies of victims were laid out on the streets of the neighbourhood.
Syrian Observatory for Human Rights chief Rami Abdel Rahman said the bombs on Aleppo city struck the rebel-held eastern neighbourhood of Al-Shaar, killing 12 people including eight members of a single family.
The casualties were all men, with the number of fatalities expected to rise due to the severity of their injuries, with a further 18 people still missing.
"People often gather on Saturday mornings at the Al-Hail market in Al-Bab, which is why the number of dead was so high," said Rahman.
"This is one of the biggest massacres that regime planes have committed since the beginning of 2015," said the Syrian Revolution General Commission activist group.
Syria's government has denied using barrel bombs – made of oil drums, gas cylinders or water tanks packed with explosives and scrap metal.
President Bashar al-Assad refused to accept his troops used barrel bombs. In a BBC interview he said the allegation was a "childish story" he said: "There are no barrel bombs. We don't have barrels."
On Friday night in Tadamon, at least six regime loyalist forces were killed and 10 wounded in an explosion on Friday (29 May), said the Observatory.
The neighbourhood has seen an influx of refugees from nearby Yarmuk, after IS militants overran the Palestinian camp in April.