The Syrian state and allied militia have detained and abducted tens of thousands of people since 2011 in a campaign of enforced disappearances that is a crime against humanity, Amnesty International said in a report on Thursday.
The rights watchdog interviewed relatives of the disappeared who said they had been forced to pay bribes to middlemen with close ties to the authorities to gain information on the fate of their family members, fuelling a lucrative black market.
Amnesty said it had attempted to engage with the Syrian authorities on the issue of forced disappearances and was awaiting a response. The Syrian government has regularly dismissed reports accusing the state of human rights abuses.
"The enforced disappearances carried out since 2011 by the Syrian government were perpetrated as part of an organized attack against the civilian population that has been widespread, as well as systematic," Amnesty said.
It described such acts as crimes against humanity and called on Damascus to allow access to international monitors from the United Nations-mandated Independent International Commission of Inquiry for Syria to seek information on detainees.
Syria's uprising started in 2011 with protests against President Bashar al-Assad and has descended into a civil war drawing in foreign states that pits a range of insurgent groups against government forces and allied militia.
More than 65,000 people, most of them civilians, were forcibly disappeared between March 2011 and August 2015 and remain missing, Amnesty said, citing figures from the Syrian Network for Human Rights, a Syria-based monitoring group.
Detainees were squeezed into overcrowded, dirty cells where disease was rampant and medical treatment unavailable, Amnesty said, saying those imprisoned suffered torture, through methods such as electric shocks, whipping, suspension, burning and rape.
"People would die and then be replaced," said Salam Othman, who was forcibly disappeared from 2011 to 2014.
"I did not leave the cell for the whole three years, not once ... Many people became hysterical and lost their minds," he was quoted as saying in the report.
Fearing what could happen to them if they make an official enquiry to the government, relatives are forced to go to middlemen to seek details on detainees, such as their location or whether they are alive, Amnesty said.
Such bribes range from hundreds to tens of thousands of dollars, with some families driven to sell their homes to come up with the sums demanded.
"State officials are profiting from enforced disappearances in Syria, and given how widespread and common these bribes are, the state must either be expressly or implicitly condoning this practice," said Nicolette Boehland, the author of the report, which only covered detentions by the state.
Amnesty said it will issue a report focused on detention-related abuses committed by non-state armed groups in the coming months.