Syrians in the besieged rebel-held area of eastern Ghouta, near Damascus, have suffered their deadliest week since 2015, according to the Syrian Observatory for Human Rights.
The monitor said government air strikes had killed more than 230 people in the last four days.
France on Friday (February 9) called on Russia to do everything it could to get its Syrian ally to ease the growing humanitarian crisis.
In a telephone call to his Russian counterpart Vladimir Putin, French President Emmanuel Macron said it was imperative that peace talks made progress and voiced his concern at signs that chlorine bombs have recently been used against civilians.
Damascus has repeatedly denied using chemical weapons, and insists its strikes only target militants.
The conflict is raging on two other fronts: Turkey is waging an offensive against Kurdish fighters in Afrin, in the northwest, while Syrian government forces are pounding the rebel-held province of Idlib.
The White Helmets, a volunteer rescue group, said its centre in Khan Shaykhun was the target of two separate air strikes that killed three of its members.
The group uploaded a video on Thursday (February 8) showing one of the group’s volunteer rescuers covered in dust and being carried out of a demolished building
Meanwhile, Turkey has been firing more rockets into Syria’s Afrin region. It's targeting Kurdish YPG militias, which it views as a terrorist group – an extension of the outlawed Kurdistan Workers Party (PKK) that has waged a deadly three-decade insurgency in Turkey.
Authorities in Afrin say at least 160 people have been killed and tens of thousands more have been displaced since the start of the offensive last month.
The YPG and its allies have set up three autonomous cantons in the north, including Afrin, since the Syrian conflict began in 2011.
Their territory has expanded since they joined forces with the United States to fight Islamic State militants - although Washington opposes their autonomy plans, as does Syrian President Bashar al-Assad's government.