'7,000 tortured or killed in detention'

New evidence has been released that up to 7,000 Syrians who died in government detention centres in Syria were tortured to death, a rights group said in a report.

Human Rights Watch released a report after an eight month research of at least 53,275 smuggled photographs of tortured Syrian individuals.

In January 2014, a defector, who was given the codename of 'Cesar', smuggled images out of Syria, showing bodies of detainees photographed by his colleagues and himself.

Cesar's role in the military police in Syria was to photograph and document the bodies of those brought from their places of detention to a military hospital.

The bodies in his images showed signs of starvation, brutal beatings, strangulation and other forms of torture and killing.

In his interview with the investigators' legal team conducted over the course of three days in January 2014, Caesar told the team he had worked in the Syrian military police for 13 years.

Most of the 6,786 victims shown in the Caesar photographs were detained by just five intelligence agency branches in Damascus.

The 86-page report, "If the Dead Could Speak: Mass Deaths and Torture in Syria's Detention Facilities," answers questions such as: are the photographs authentic? Are they really images of dead detainees? If so, what caused so many to die? and how did the bodies end up in military hospitals and what happened to the corpses afterwards?

The Syrian Network for Human Rights (SNHR), a group monitoring the war, documented the arrest and detention of more than 117,000 people in Syria since March 2011.

SNHR documented at least 11,358 deaths in detention as of June 26, 2015. The total number is likely higher given that many cases go unreported.