Syrian government forces are waging a systematic campaign of enforced disappearances to terrorise the population, amounting to a crime against humanity, a UN-mandated probe said Thursday.
"Enforced disappearances are perpetrated as part of a widespread campaign of terror against the civilian population," the Independent International Commission of Inquiry said in a report.
"There are reasonable grounds to believe that enforced disappearances were committed by government forces as part of a widespread and systematic attack against the civilian population, and therefore amount to a crime against humanity," it added.
Syrian regular forces and allied militias launched the campaign as protests against the regime of President Bashar al-Assad broke out in March 2011, said the commission, which includes former war crimes prosecutor Carla del Ponte.
The actions have left anguished families not knowing if their loved ones are detained or dead.
The commission said that in 2011 through to early 2012, the majority of those who disappeared were men aged between 16 and 40 who were seized at demonstrations.
Since then, the net has widened, with mass arrests and targeted detentions of people such as relatives of known rebels and civilians living in opposition areas.
Patients from rebel-held zones who had to seek medical care in government-controlled areas were seized in hospitals, the commission added.
And medical staff were grabbed in an apparent attempt to punish them for working in opposition areas and deterring others from doing so.
The commission did not estimate the overall number of disappeared Syrians nor detail named cases, but a source familiar with the probe said it had documented over 100 cases.
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"These numbers only represent a fraction of all cases of enforced disappearances in Syria. The commission has reason to believe that there are thousands," the source told AFP.
In September, the International Committee of the Red Cross, which specialises in tracing the missing in war zones, said that "untold numbers" had disappeared in Syria.
It said it had received over 1,000 requests from desperate relatives trying to find family members, with 800 thought to be detained, and the numbers were likely the tip of the iceberg.
The commission said individuals who seek news of missing relatives themselves risk arrest, creating a "climate of fear" that compounded the "systematic refusal" of the authorities to disclose the fate of their loved ones.
Often the only option was to try to obtain information from released detainees, or bribe middlemen, the report said.
The commission, headed by Brazilian Paulo Sergio Pinheiro, was created in 2011 by the UN Human Rights Commission.
It has issued a string of reports accusing the Syrian regime and rebels of war crimes, and has drawn up a confidential list naming suspected perpetrators.
Its disappearances report included evidence from Syrian military defectors.
The commission also examined rebel actions, saying that kidnappings carried out by some groups were sowing fear but did not "amount to enforced disappearances as the fate of the victims is not denied or concealed".
Such kidnappings could however constitute a war crime, it said.
It also warned that the hardline Al-Qaeda group the Islamic State of Iraq and the Levant (ISIS) had "begun to adopt practices, such as incommunicado detention, that may lead to disappearances".