Former detainees and defectors have described details of 27 detention facilities run by Syrian intelligence agencies, accusing authorities of ill-treatment and torture.
“The intelligence agencies are running an archipelago of torture centres scattered across the country,” said Ole Solvang, emergencies researcher at Human Rights Watch.
"The systematic patterns of torture documented clearly point to a state policy of torture and ill-treatment and therefore constitute a crime against humanity."
The 81-page HRW report, Torture Archipelago: Arbitrary Arrests, Torture and Enforced Disappearances in Syria’s Underground Prisons since March 2011, is based on more than 200 interviews conducted by HRW since March 2011.
The report includes maps locating the detention facilities, video accounts from former detainees, and sketches of torture techniques described by people who witnessed or experienced torture.
HRW called on the UN Security Council to refer the situation in Syria to the International Criminal Court and to adopt targeted sanctions against officials credibly implicated in the abuses.
The facilities cited in the report are those for which multiple witnesses have indicated the same location and provided detailed descriptions of torture.
The report says the actual number of detention facilities used by intelligence agencies is probably much higher.
Almost all the former detainees interviewed by HRW said they had been subjected to torture or witnessed the torture of others during their detention.
Interrogators, guards, and officers used a broad range of torture methods, including prolonged beatings, often with objects such as batons and cables, holding the detainees in painful stress positions for prolonged periods of time, the use of electricity, burning with acid, sexual assault and humiliation, the pulling of fingernails, and mock execution.
Altogether HRW documented more than 20 distinct torture methods used by the security and intelligence services.
In most cases former detainees were subjected to a range of these torture methods.
Assad regrets shooting down of Turkish jet
Meanwhile, Syrian President Bashar al-Assad has told a Turkish newspaper he wished Syrian forces had not shot down a Turkish jet last month.
He said he would not allow the tensions between the two countries to turn into open combat.
"We learned that it [the plane] belonged to Turkey after shooting it down.
“I say 100% 'if only we had not shot it down'," the Cumhuriyet newspaper quoted Mr Assad as saying in an interview published today.