An Amnesty international revealed that Syrian government executed thousands of prisoners in mass hangings and carried out systematic torture at a military jail near Damascus.

Amnesty international said executions took place between 2011 and 2015, but were probably still being carried out and amounted to war crimes.

Syria’s government and President Bashar al-Assad have rejected similar reports in the past of torture and extrajudicial killings in a civil war that has claimed hundreds of thousands of lives.

The amnesty report said that between 5,000 and 13,000 people were executed at Sednaya.

Lyn Maalouf, the deputy director for research at amnesty international’s regional office in Beirut said that the findings of the report were about a systematic campaign of mass hanging.

Every week, usually on Mondays and Wednesdays, groups of detainees, of between 20 to 50 detainees, would be taken from their cells, told that they would be transferred to civilian detentions but instead of that, they were taken to a cell in another building inside of Sednaya where they would be hanged.

Maalouf said amnesty international was calling on the United Nations to launch an independent and transparent investigation into what is taking place in Sednaya.

The report concluded prisoners, who included former military personnel suspected of disloyalty and people involved in unrest, underwent sham trials before military courts.

Amnesty report was based on interviews with 84 witnesses including former guards and officials, detainees, judges and lawyers, as well as experts on detention in Syria.