BEIRUT (AFP) - A series of barrel bombs dropped from Syrian regime helicopters killed at least 45 civilians and wounded dozens on Saturday in the northern province of Aleppo, a monitoring group said.

"At least 45 civilians were killed, and dozens were wounded, when regime helicopters dropped barrel bombs on the city of Al-Bab and in an eastern neighbourhood of Aleppo," said the Syrian Observatory for Human Rights.

Observatory head 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 other 33 civilians, all male, were killed at a market in Al-Bab, Abdel Rahman told AFP.

Al-Bab lies about 40km northeast of Aleppo city and is controlled by the extremist Islamic State group.

"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 Abdel Rahman.

Those killed were all male because women have much less freedom of movement in IS-controlled areas, he added.

The Observatory said the death toll in Al-Bab was likely to rise, as many wounded civilians were in critical condition and another 18 were still unaccounted for.

Barrel bombs are crude weapons made of oil drums, gas cylinders or water tanks packed with explosives and scrap metal that are usually dropped from helicopters.

The Syrian government's use of the weapons has come under fire by rights groups, who say barrel bombs are indiscriminate and often kill many civilians.