After more than two years of ISIS occupation, a church in Qaraqosh held its first service on Sunday.

Surrounded by charred walls and in front of a ruined altar, dozens of Iraqi Christians celebrated mass at the Church of the Immaculate Conception.

Church bells rang out in the town on the southeastern approaches to Mosul where Iraqi troops, backed by US-led air and ground forces, have been driving back the Sunni Muslim jihadists ahead of a battle for the city itself.

"Today Qaraqosh is free of Daesh (Islamic State)," Syriac Catholic Archbishop of Mosul Butrus Moshe – who was born in the town – told worshippers.

"Our role today is to remove all the remnants of Daesh," he added. "This includes erasing sedition, separation and conflicts, which victimized us.

"Political and sectarian strife, separating between one man and another, between ruler and follower, these mentalities must be changed."

Qaraqosh once had the largest Christian population in Iraq, and was home to at least a quarter of the country's Christian community.

However, Kurdish troops stationed to protect the town withdrew on August 6, 2014, leaving ISIS free to move in overnight and take it along with three other Christian-majority towns.

Tens of thousands of people were then forced to flee after ISIS issued an ultimatum to Christians: leave, convert to Islam, pay a heavy tax or be killed.

The town was liberated as part of the Mosul offensive over the past two weeks.

Additional reporting by Reuters.