A damning report by human rights group Amnesty International claims that at least 13,000 executions took place at Saydnaya prison in Syria between September 2011 and December 2015.
The rights group says the alleged executions were authorised at the highest levels of the Syrian government of Bashar al-Assad.
The government has previously denied killing or mistreating detainees.
However, UN human rights experts said last year that witness accounts and documentary evidence strongly suggested that tens of thousands of people were being detained and that “deaths on a massive scale” were taking place in custody.
Amnesty interviewed 84 people, including former prison guards, detainees and government officials at Saydnaya prison for its research.
It claims that every week, and sometimes twice a week, groups of between 20 and 50 people were hanged in secrecy at the prison located in north of Damascus.
Prior to their execution, prisoners were brought before a “military field court” in the Damascus district of Qaboun for “trials” lasting between one and three minutes, the report alleged.
A former military court judge quoted in the report said prisoners would be questioned if they had committed crimes alleged to have taken place. “Whether the answer is ‘yes’ or ‘no’, he will be convicted… This court has no relation with the rule of law,” he said.
The report also states that prisoners were informed on the day of the execution that they would be transferred to a civilian prison then taken to a basement cell and beaten over a period of two or three hours.
The detainees would then be blindfolded in the middle of the night and moved to another part of the prison, where they were taken into a room in the basement and told they will be executed just moments before nooses were placed around their necks, the report adds.
The bodies of the deceased were allegedly then loaded onto lorries, and transferred to Tishreen military hospital in Damascus for registration and burial in mass graves located on military land.
On the basis of evidence of the testimony of its witnesses, Amnesty estimates that between 5,000 and 13,000 people were executed at Saydnaya for a five year period since 2011.
Although Amnesty does not have evidence of hangings taking place since December 2015, the rights group says it has no reason to believe they have stopped, and that thousands more were likely to have been executed.
Amnesty says these practices amounted to war crimes and crimes against humanity.
It also added that capital punishment sentences have to be authorised by the grand mufti and by either the army’s chief of staff or the defence minister, who are delegated to act on behalf of Bashar al-Assad.
Amnesty says it contacted the Syrian authorities about the allegations last month but has received no response.
In August 2016, Amnesty reported that at least 17,723 people had died in custody as a result of torture and the deprivation of food, water and medical care between March 2011 – when the revolution began – and December 2015. That figure did not include those allegedly executed at Saydnaya prison.
This short video about torture at Saydnaya prison was posted on YouTube by Amnesty International in August 2016.