MOSUL, Iraq (Reuters) -- Young volunteers have been clearing dust and debris from St. Thomas church in Mosul, as the Iraqi city occupied by Islamic State militants seeks to sweep away the horrors of a brutal three-year rule and welcome back members of minority faiths.

The Syriac Catholic church, dating from the mid-1800s, was looted by the hardline Islamist movement after it invaded Mosul in 2014 and has been abandoned ever since. The militants were finally driven out of Iraq's second largest city in 2017.

"This is a message to say 'Come back, Mosul is not complete without you'," said Mohammed Essam, co-founder of a local volunteer group, after a day of cleaning rubble and dirt from the floors of the church and the courtyard outside.

There are still reminders of Islamic State's occupation.

The words "Land of the Caliphate" are painted in Arabic script on one wall, a reference to the group's ambition of carving out its own territory across the Middle East.

Until the fall of Saddam Hussein in 2003, about 45,000 Christians lived in Mosul, Father Raed Adel, in charge of the city's Syriac Catholic churches, told Reuters.

Their numbers kept dwindling, and the Christians who were left fled the area when Islamic State fighters took over in June, 2014.

Essam remained and witnessed atrocities committed against religious minorities by the militants.

"We want to change the perception people in the region and beyond have about Mosul," he explained. "We want to say that Christians belong here. That they have a rich history here."

Since the liberation, the "Sawaed al-Museliya" (Arms of Mosul) volunteer group has provided community services including emergency food support and raising funds for rebuilding homes belonging to the city's poorest residents.

By clearing up the church, they want to support the local Christian community's efforts to restore damaged properties and also reassure Christians who fled.

"Even though they left, we are committed to take care of them and of their places of worship," Essam said.

On the other side of the city, Father Adel holds a Sunday service in Mosul's main operating church of Bishara.

"Since the city was liberated from ISIS, there is a new mentality among people originally from Mosul, including Muslims. This encourages the return of Christians, even though it is a modest return. But it is a first step along a long path."

Only about 50 Christian families have returned to live in the city so far, although more come to work or study each day, crossing from Iraq's northern Kurdistan region where they found refuge in 2014, Father Adel said.

"Our youth are the hope of this city after it suffered so many difficulties and problems," Father Adel said. "It was in a tunnel of darkness."

Additional reporting and writing by Charlotte Burenau; Editing by Mike Collett-White.