Detainees held by the Syrian government are dying on a massive scale amounting to a state policy of extermination of the civilian population, a crime against humanity, United Nations investigators has said.

The UN commission of inquiry called on the security council to impose sanctions against Syrian officials in the civilian and military hierarchy responsible for or complicit in deaths, torture and disappearances in custody, but stopped short of naming individuals.

In their report released on Monday, the independent experts said they had also documented mass killings and torture of prisoners by two jihadi groups, al-Nusra Front and Islamic State, constituting war crimes.

“Over the past four and a half years, thousands of detainees have been killed while in the custody of warring parties,” the commission of inquiry on Syria said.



“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. There are reasonable grounds to believe that the conduct described amounts to extermination as a crime against humanity.”

Tens of thousands of detainees are held by President Bashar al-Assad’s government at any one time, and thousands more have “disappeared” after being arrested by state forces or gone missing after abduction by armed groups, the report said.

Through mass arrests and killing of civilians, including by 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.

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.

Isis and al-Nusra Front have committed mass killings of captured government soldiers and subjected civilians to “illicit trials” by sharia courts which ordered death sentences, the report said.

“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.