The remains of at least 20 bodies have been found in a grave in east Lebanon, near the former headquarters of the Syrian army intelligence, police say.
Many Lebanese disappeared during the 29 years of Syrian domination
Excavation teams are continuing work at the grave in the Bekaa Valley and bodies are being taken for DNA testing.
The mass grave is near a former Syrian-run prison, where many Lebanese detainees were held.
Correspondents say dozens of Lebanese disappeared during Syria's 29 years of military presence.
The Syrian army withdrew in April, after Lebanese and international pressure following the assassination of former Lebanese Prime Minister Rafik Hariri.
It is unclear why digging started at the site on a hillside in the town of Anjar, near the Syrian border.
Some reports suggest the bodies were buried about 12 years ago.
Witnesses said one was dressed in a military uniform.
Lebanese detainees on their way to Syrian jails passed through the prison and those who died under torture were buried on the site, the BBC's Kim Ghattas reports from Beirut.
Another 24 bodies were found last month in a mass grave near the Lebanese ministry of defence, east of the capital.
Most of the bodies belonged to Lebanese soldiers who fought against the Syrian army at the end of Lebanon's civil war in 1990.
Syrian troops moved in shortly after the conflict started in 1975.
They pulled out after growing international pressure including a UN Security Council resolution and anti-Syrian street protests, sparked by Mr Hariri's murder in February.
A UN investigation has implicated several Syrian officials, but Syria has denied any involvement in the killing.