Scores of Christians were killed by ISIS during the group's occupation of al-Qaryatain, it has emerged.

The Syrian Orthodox Patriach has told of the horrific treatment Christians suffered under ISIS rule in the town, which was re-captured by the Russian-backed Syrian army last week.

When Islamic State militants swept through al-Qaryatain in August 2015, 21 Christians were murdered, Patriarch Ignatius Aphrem II told the BBC. Prior to the war, al-Qaryatain was home to an estimated 2,000 Christians but most had fled by the time ISIS took control, leaving around 300 behind.

Some were killed trying to escape while others were executed for breaking their "dhimmi" contracts. This was an agreement forced upon those who remained in the town and required them live according to a strict interpretation of Sharia law.

After al-Qaryatain was retaken by government forces on April 3, reports are emerging of what life was like under the rule of ISIS. Much of the town is devastated – many buildings, including a 1,500-year-old Catholic monastery, have been ruined.

If President Bashar al-Assad's forces can reassert full control over al-Qaryatain it would be another major blow to ISIS. The jihadist group has lost the ancient city of Palmyra as well as substantial territory in northern Iraq in recent weeks.

Syrian government coaches have already begun bringing thousands of civilians back to al-Qaryatain and Palmyra, which lie about 60 miles apart.

Patriarch Aphrem said his priority was to restore peace among different faith groups after ISIS' rule.

"We lived this situation for centuries, we learned how to respect each other, we learned how to live with each other," he said. "We can live together again, if we are left alone by others."

A ceasefire in Syria has led to a drop in fighting. However, ISIS and the al-Qaeda linked Nusra Front have been excluded from the deal and are still being targeted.