The site, near the Adra industrial area northeast of the capital, is less than 20 kilometres from the Saydnaya prison.
Diab Serriya, from the Association of Detainees and Missing Persons of Saydnaya Prison, said the site was first identified in 2019 through “testimony of an intelligence personnel member who had deserted”.
Satellite imagery suggests the site was in use from 2014, he said.
“Probably this grave contains detainees but also former regime or opposition fighters killed in battle,” he told AFP by telephone.
The notorious Saydnaya complex, the site of extrajudicial executions, torture and forced disappearances, epitomised the atrocities committed against Assad’s opponents.
Serriya said “the bags of bones were probably brought from other graves”, adding that “the road to discovering who is buried here will be long”.
The doors of Syria’s prisons were flung open after a militant-led rebel alliance ousted Assad this month, more than 13 years after his brutal repression of anti-government protests triggered a war that would kill more than 500,000 people.
The fate of tens of thousands of prisoners and missing people remains one of the most harrowing legacies of the conflict.
Mohammed Ali from the Adra municipal council denied residents were aware of the site, which is located near a Syrian army facility.
“It was forbidden to approach it or take photos as it was a military zone,” he told AFP.
