BEIRUT, Jumada I 10, 1438, Feb 7, 2017, SPA -- Syrian regime's authorities have killed as many as 13,000 people, possibly more, since the start of the 2011 uprising in mass hangings at a prison north of Damascus known to detainees as "the slaughterhouse," Amnesty International said on Tuesday. In a new report covering the period from 2011 to 2015, Amnesty said 20-50 people were hanged each week at Saydnaya Prison in killings authorized by senior Syrian officials, including deputies of Bashar Assad's regime, and carried out by military police. The report referred to the killings as a "calculated campaign of extrajudicial execution." Amnesty has recorded at least 35 different methods of torture in Syria since the late 1980s, practices that only increased since 2011, said Lynn Maalouf, deputy director for research at Amnesty's regional office in Beirut. Other rights groups have found evidence of massive torture leading to death in Syrian detention facilities. In a report last year, Amnesty found that more than 17,000 people have died of torture and ill-treatment in custody across Syria since 2011, an average rate of more than 300 deaths a month. Those figures are comparable to battlefield deaths in Aleppo, one of the fiercest war zones in Syria, where 21,000 were killed across the province since 2011. "The horrors depicted in this report reveal a hidden, monstrous campaign, authorized at the highest levels of the Syrian regime, aimed at crushing any form of dissent within the Syrian population," Maalouf said. While the most recent data is from 2015, Maalouf said there is no reason to believe the practice has stopped since then, with thousands more probably killed. "These executions take place after a sham trial that lasts over a minute or two minutes, but they are authorized by the highest levels of authority," including the Grand Mufti, a top religious authority in Syria, and the defense minister, she said. --SPA 10:12 LOCAL TIME 07:12 GMT www.spa.gov.sa/w327121