WASHINGTON — The State Department released satellite images on Monday that officials said showed that President Bashar al-Assad of Syria has built a crematory at a military prison outside Damascus to hide a large number of executions.
Stuart E. Jones, the acting assistant secretary of state for Near Eastern Affairs, said officials believed that the crematory had been constructed so that little evidence exists of the thousands of people who are executed every year at the Sednaya Prison complex.
The evidence presented by the United States remains circumstantial. Satellite photographs of the complex show that while nearby buildings were covered in snow, the roof of the building suspected to be a crematory was free of snow, suggesting a significant internal heat source. Officials also said that a discharge stack, and architectural elements thought to be a firewall and air intake, were consistent with a crematory.
Mr. Jones said that prisoners had in the past been buried in mass graves, but that a crematory could dispose of bodies without leaving evidence behind.
Amnesty International recently reported that, since 2011, thousands of civilians had been executed in mass hangings at the prison, some carried out at night in an attempt to maintain secrecy.
The prison complex is about 45 minutes north of Damascus.
The timing of the public announcement suggested that the Trump administration was pressing a tougher political line on Syria, and seeking to embarrass Russia and Iran — which have supported the Assad government — in an effort to press the Syrian leadership to engage in substantive negotiations.
The State Department’s release of the photographs came a day before a new round of negotiations on the Syria crisis is to begin in Geneva on Tuesday.