The United States has accused the Syrian government of carrying out the mass execution of thousands of prisoners
The US says around 50 detainees a day are being hanged at the Sednaya military prison outside Syria's capital of Damascus.
The bodies are reportedly then burned in a large crematorium to hide the extent of the killings.
A recent Amnesty International report called the prison a "human slaughter-house".
Around 13,000 prisoners are thought to have been killed there.
The United States says it has evidence Syrian President Bashar al-Assad's regime has built the crematorium near the site of the prison, a State Department official says.
Stuart Jones, the acting assistant secretary for Near Eastern Affairs, said on Monday the crematorium could be used to dispose of bodies near a prison where tens of thousands of people have been detained during the country's six-year-old civil war.
Jones also said the United States has "reason to be skeptical" about a deal to set up "de-escalation zones" brokered by Russia during ceasefire talks in the Kazakh capital Astana last week.
Reuters / Newshub.