At least 35 civilians were killed and dozens were injured by Syrian regime attacks in Syria's Eastern Ghouta, Syrian civil defence forces said on Tuesday.
According to sources, the casualties are expected to rise as the regime attacks are continuing.
Eastern Ghouta, which houses around 400,000 residents has remained under a crippling regime siege for the last five years, the Anadolu news agency reported.
In May last year, Russia, Iran and Turkey signed an agreement to set up de-escalation centres, in order to reduce violence and airstrikes in some parts of Syria.
De-escalation zones include the Idlib Province, some parts of Latakia, Hama and Aleppo Provinces, Homs, Eastern Ghouta, Daraa and al-Quneitra Provinces in southern Syria.
Syria has been embroiled in a civil war since 2011.
Protestors have for long been demanding the resignation of Syrian President Bashar al-Assad over his autocratic rule.