More barrel bombs were dropped on the northern Syrian city of Aleppo Saturday, killing at least 20 people, the Syrian Observatory for Human Rights said.
The raids came as Al-Qaeda affiliate Al-Nusra Front and allied Islamist rebel groups launched a new offensive against the jihadist Islamic State of Iraq and the Levant (ISIL) in the east of the country.
The Observatory two children were among those killed in separate barrel bomb attacks on Aleppo's eastern rebel-held neighbourhoods.
Hundreds of people have died in several waves of barrel bomb assaults, each lasting several days, since December 15, the Britain-based group says.
Thousands of people have fled the areas being targeted.
The raids came as government forces pressed an advance into the east and north of Aleppo, large swathes of which fell to rebels after a massive offensive in July 2012.
Rights groups have condemned the regime's use of barrel bombs as indiscriminate.
Helicopters also dropped barrel bombs on Daraya, a rebel bastion southwest of Damascus, which has been under siege for more than a year.
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And in Daraa province in southern Syria, 16 people were killed, the Observatory said.
Among them were three rebels, and 13 civilians, including six children, who died in four different attacks on several parts of the province.
Al-Nusra Front and rebel brigades, including the powerful Ahrar al-Sham, launched a new offensive in the eastern province of Deir Ezzor against their erstwhile ally ISIL, the Observatory said.
ISIL was once welcomed by rebels battling President Bashar al-Assad, but abuses by the group turned much of the opposition against them.
Saturday's offensive comes just over a month after three massive rebel alliances declared war against ISIL in much of the north.
Both Al-Nusra and ISIL grew out of Al-Qaeda in Iraq, but have split in Syria.
More than 1,800 people, mostly fighters, died in January fighting between rebels and ISIL.
Saturday's clashes come a day after ISIL took over several rebel bases in Hasakeh province, north of Deir Ezzor.
Both Deir Ezzor and Hasakeh are strategic because they lie on the Iraqi border.
Deir Ezzor is a key conduit for ISIL to send weapons and fighters from Iraq into Syria.