Eastern Ghouta, located just east of Damascus, has become the recent focus of a fierce offensive by Syrian President Bashar al-Assad’s forces.
In just over a week, more than 500 civilians have been killed, according to the UK-based Syrian Observatory for Human Rights.
The rebel-held enclave, which was besieged by the government in 2013, is home to about 400,000 people.
Health officials have also accused the Syrian government of using chlorine gas in their aerial bombardment campaign on Eastern Ghouta.
The UN has called the situation in the enclave “hell on earth”.
Hundreds of thousands of people have died in fighting during Syria’s seven-year civil war, and millions have been forced to flee the country.