Syria's transitional authorities have discovered a mass grave with the remains of at least 170 people near the town of Al Otaiba.
The bodies are believed to be those of people killed in an ambush in 2014, while trying to flee the siege of Eastern Ghouta by forces loyal to Bashar Al Assad, president at the time, a prosecutor told state news agency Sana
The siege during the civil war was notorious for the use of chemical weapons by Al Assad's forces.
The Assad regime and Iran-backed militias aligned with it claimed the ambush led by Hezbollah operatives was carried out on fighters from the Nusra Front, an Islamist rebel group.
However, the Syrian Human Rights Committee cast doubts on these claims.
Syrian President Ahmad Al Shara led the Nusra Front, which evolved into Hayat Tahrir Al Sham and toppled the Assad regime in a rebel offensive in December.
Judge Mohammed Omar Hajar said authorities were alerted to the human remains by a shepherd. Authorities found skulls, bones, and skeletons at the site, belonging to what they said were civilian victims of the former regime.
He said the ambush involved the detonation of landmines, followed by direct gunfire at civilians. The bodies were then randomly buried in a long trench using heavy machinery in an area thickly covered with mud and reeds, it is claimed.
Syrian authorities have launched an investigation into the matter, reported Sana, and work is under way to recover the bodies and enable families to identify loved ones.
Judge Hajar told Sana that "this crime represents one of the most heinous crimes ever committed against civilians and demands the highest levels of accountability and justice".
Since the fall of Al Assad last year, many mass graves have been uncovered across the country. About 150,000 people remain unaccounted for as a result of the civil war, according to the International Commission on Missing Persons.
Hezbollah fought on behalf of the Assad government during the Syrian civil war that began in 2011. But as the Lebanese group reeled from a war with Israel last year, it could not rescue him from being overthrown in a rebel offensive in December.
Hezbollah leader Naim Qassem initially signalled an open mind towards Syria's new rulers, saying Hezbollah "cannot judge these new forces until they stabilise". But Mr Al Shara's government has since accused Hezbollah of working with traffickers of drugs and weapons at the Lebanese border.
Last week, Syria's new authorities arrested suspected members of Hezbollah in a raid in the Damascus countryside. Officials said rocket launchers and ammunition were seized from a cell plotting attacks inside Syria.
