Amnesty International estimates that 17,723 people died in Syrian regime jails between March 2011 and December 2015.
More than 17,723 people have died in Syrian regime jails between the start of the country's civil war in March 2011 and December 2015, Amnesty International said in a report that was released on Thursday.
This is an average rate of more than 300 deaths each month, or about 10 people each day, Amnesty said.
The report named "It breaks the human" was based on interviews with 65 "torture survivors" who described the inhuman conditions and rights abuses taking place in regime-operated facilities across the country.
The survivors said the abuse began before they set foot in a detention centre upon their arrest and during transfers.
Behind closed doors, detainees are first subjected to what they call a "welcome party," a ritual in which they are beaten by guards using silicone or metal bars and electric cables.
This is frequently followed by "security checks" in which female detainees in particular are subjected to systematic rape and sexual assaults by guards.
"They treated us like animals. They wanted people to be as inhuman as possible. I saw the blood, it was like a river. I never imagined humanity would reach such a low level. They would have had no problem killing us right there and then," said Samer, a lawyer arrested near Hama.
In addition to relentless torture and maltreatment, detainees also face poor living conditions, suffering from a lack of food, limited medical care, and inadequate sanitation in overcrowded prisons.
Survivors described being held in cells so overcrowded that they had to take turns to sleep, or sleep while squatting.
"It was like being in a room of dead people. They were trying to finish us there," a former detainee said while describing the cell he was held in.
Amnesty called on the Syrian regime to stop using torture to silence its opponents and to provide independent monitors with access to all places of detention. It also demanded all prisoners to be released or promptly tried in line with international fair-trial standards.
"For decades, Syrian government forces have used torture as a means to crush their opponents," Amnesty's Middle East and North Africa Director Philip Luther said.
"Today, it is being carried out as part of a systematic and widespread attack directed against anyone suspected of opposing the government in the civilian population and amounts to crimes against humanity," he added.
"Those responsible for these heinous crimes must be brought to justice.",
Reports of the Syrian regime using torture to get information or to silence dissent date back to the era of Hafez al Assad, who ruled Syria for 30 years until his death in 2000, only for his son Bashar al Assad to take over.
More than 17,000 detainees disappeared in the late 1970s and early 1980s.
According to the Syrian Network for Human Rights (SNHR), more than 215,000 people have been detained since the beginning of the Syrian uprising.
In March 2011, Syrians started an uprising against the Assad regime, calling for freedom, dignity and better living conditions. However, it later evolved into a civil war in which hundreds of thousands of people have been killed and nearly half of the country's population has been displaced.