Jones then said that the State Department believes that thousands of detainees in the Saydnaya military prison near Damascus, the nation's largest facility of its kind, are being executed in mass hangings.
Newly declassified information found that at least 50 detainees each day are executed in prison, said Stuart Jones, an Obama administration appointee who is the acting assistant secretary of state for Near Eastern Affairs.
Crematoria were used by Adolf Hitler of Nazi Germany to burn the bodies of his Jewish victims, once the sheer scale of murders rendered the use of mass graves insufficient.
"We believe that the building of a crematorium is an effort to cover up the extent of mass murders taking place in Saydnaya prison", Stuart Jones, the top USA diplomat for West Asia, told reporters.
The department released commercial satellite photographs showing what it said was a building in the prison complex that had been modified to support the crematorium.
The Donald Trump administration on May 15 accused Bashar al-Assad's regime of building a crematorium at the Saydnaya prison complex outside Damascus in an effort to destroy evidence of mass murder.
"Beginning in 2013, the Syrian regime modified a building within the Saydnaya complex to support what we believe is a crematorium", said Jones, now an acting assistant secretary of state. The non-binding measure, which passed 392-3, denounced a litany of crimes perpetrated by the Assad regime, including having committed "widespread torture and rape, employed starvation as a weapon of war, and massacred civilians, including through the use of chemical weapons, cluster munitions, and barrel bombs;..."
Moreover Jones called on Russian Federation and Iran, whom he described as Assad's "closest allies", to "press for an end to these murderous detention policies".
The satellite images show what it said is a building in the prison complex that has been modified to support a large-scale crematorium.
Granted, before the Syrian Civil War, it wasn't crystal clear that Bashir Assad would become one of the globe's bloodiest and most ruthless dictators. "A key point that took place in that bilateral meeting was telling Russian Federation to use its power to rein in the regime".
Opposition representatives have demanded Assad's removal.
The allegation came as President Donald Trump is weighing options in Syria, where the US attacked a government air base last month in response to an alleged chemical weapons attack on civilians.
Jones said that despite the talks last week between Tillerson and Lavrov, he "would not say they have mapped a way forward on how to address Syrian atrocities or how to move forward on the Geneva process", which is meant to help establish a political settlement to the conflict.