Detainees held by the Syrian regime are dying on a massive scale amounting to a state policy of "extermination" of the civilian population, a crime against humanity, United Nations investigators said on Monday.
The UN commission of inquiry called on the Security Council to impose "targeted sanctions" on Syrian officials in the civilian and military hierarchy responsible for or complicit in deaths, torture and disappearances in custody, but stopped short of naming them.
The report, "Out of Sight, Out of Mind: Deaths in Detention," covers March 10, 2011 to November 30, 2015. It is based on interviews with 621 survivors and witnesses and evidence gathered by the team led by chairman Paulo Pinheiro.
"Over the past four and a half years, thousands of detainees have been killed while in the custody of warring parties," said the Commission of Inquiry on Syria.
The so-called "Caesar Report" released in early 2014, for instance, contained some 55,000 photographs depicting the tortured and abused bodies of around 11,000 people it said had died in Syrian jails during the first two years of the conflict.
"The killings and deaths described in this report occurred with high frequency, over a long period of time and in multiple locations, with significant logistical support involving vast State resources," the report said. "There are reasonable grounds to believe that the conduct described amounts to extermination as a crime against humanity."
Most of the detainees known to have died are men, but women and children as young as seven have also perished while being held by the Syrian authorities, the report said.
Abuse, squalid conditions and a "high frequency" of deaths were consistent across places of detention and over time, and must have been condoned up the chain of command, it wrote.
Independent experts said in the report that they had also documented mass executions and torture of prisoners by two groups in Syria, Nusra Front and the terrorist group DAESH, constituting war crimes.
Names kept in UN safe
Tens of thousands of detainees are held by Syrian regime leader Bashar al Assad at any one time, and thousands more have "disappeared" after arrest by state forces or gone missing after abduction by armed groups, it said.
Through mass arrests and killing of civilians, including starvation and untreated wounds and disease, state forces have "engaged in the multiple commissions of crimes, amounting to a systematic and widespread attack against a civilian population."
There were reasonable grounds to believe that "high-ranking officers," including the heads of branches and directorates commanding the detention facilities and military police, as well as their civilian superiors, knew of the deaths and of bodies buried anonymously in mass graves.
They are thus "individually criminally liable," the investigators said, calling again for Syria to be referred to the prosecutor of the International Criminal Court (ICC).
Over the past four years, the investigators, who include former ICC prosecutor Carla del Ponte, have drawn up a confidential list of suspected war criminals and units from all sides, which is kept in a UN safe in Geneva.
"Accountability for these and other crimes must form part of any political solution," the investigators said, five days after UN-sponsored peace talks were suspended without any result.
The war in Syria started as demonstrations against the Assad regime in 2011, but descended into a civil war between five main factions - the regime, the opposition, Al Qaeda affiliate Nusra Front, DAESH, and Kurdish YPG militants.
The UN estimates the death toll in Syria to be at least 250,000, while Britain based monitor Syrian Observatory for Human Rights puts the number over 260,000.
A further estimate of 350,000 refugees have sought asylum in European Union countries while about 4 million others took refuge in neighbouring countries of Turkey, Lebanon, Iraq and Egypt, with Turkey hosting the largest group with over 2.5 million.
Thousands are still pushing towards EU countries, which has caused a global refugee crisis urging for an immediate solution in Syria.