BEIRUT — Hundreds of men have disappeared after fleeing rebel-held districts in the Syrian city of Aleppo, the United Nations said Friday, amid claims that armed groups on both sides have abducted and even killed civilians who tried to leave.

Tens of thousands of people have flooded out of east Aleppo since forces loyal to President Bashar al-Assad began a final push to retake the city.

In the rebel-held east, as many as 250,000 people had held out for four years through bombardment and siege, often basing that decision on fears of retribution if they left. But after Syrian and Iran-backed pro-Assad fighters swept through three-quarters of the rebel enclave in an offensive that began Nov. 15, most residents no longer had a choice.

Syrian army officials inspect the Old City of Aleppo after regaining full control of it.(Reuters)

“Given the terrible record of arbitrary detention, torture and disappearances, we are of course deeply concerned,” he said.

The Syrian Observatory for Human Rights, a monitoring group, estimates that some 80,000 people have left rebel areas in recent weeks as government forces advanced. Reports suggested that men of fighting age were being separated from their groups by soldiers or militiamen, and that some were being taken to a nearby airport for interrogation.

Featured image courtesy of Reuters.

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