A town that once had the largest Christian population in Iraq may soon be liberated from Islamic State, according to local reports.

Forces entered Qaraqosh, which was before ISIS home to at least a quarter of Iraq's Christian community, on Tuesday and began the battle for liberation.

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

The insurgency happened less than a month after ISIS overran nearby Mosul, which is now the subject of a major offensive led by Iraqi troops backed by the US and other forces.

The battle to retake Mosul began on Monday, and the army has already secured 20 villages on the outskirts of the city.

Fraternité en Irak, an organisation set up in 2011 to help victims of religious violence in Iraq, reported on Tuesday that Peshmerga forces had entered both Qaraqosh and nearby Karamless.

"Qaraqosh and Karamless were taken this morning," the group wrote on Twitter, noting that it would take some time for military forces to establish control of the city.

A source from the Nineveh Operations Command of the Iraqi military told the BBC that troops had "entered Qaraqosh without meeting any resistance".

However, an Iraqi general told the BBC that reports Qaraqosh had been retaken were untrue.

There are believed to be no Christians left in the city after tens of thousands fled when ISIS took over.

Father Nageed Michaeel, a Dominican priest, was among those who left Qaraqosh in 2014, walking 40km on foot to Erbil in the middle of the night with around 50,000 others.

"It was terrible. There were women and children with no food and water," he previously recalled of the journey in an interview with Kurdish news agency Rudaw.

Of the situation in Erbil, he warned that the tens of thousands left stranded were getting desperate. "We are in a tunnel and cannot see the light," he said.

In December 2014, an Iraqi priest told the Sunday Times that Bahnam Wa Sara and Al Kiama churches in Qaraqosh were being used by ISIS to hold prisoners.

"These two churches are being used as prisons and for torture," Abu Aasi said, speaking from Baghdad where he had fled.

"Most inside are Christians and they are being forced to convert to Islam. ISIS have been breaking all the crosses and statues of Mary."

Despite intense persecution, however, there have been incredible stories of forgiveness from those forced to flee. Speaking to SAT-7 in March, a 10-year-old girl from Qaraqosh, Myriam, said she would ask God to forgive the militants who threatened her family's life.

"God loves everybody," she said. "I'm not angry with God because we left Qaraqosh, I thank him because he provided [for] us. Even if we're suffering here, he provides for us." She ended her interview – which has been watched hundreds of thousands of times online – with a song about how much she loves Jesus.

Another priest who fled Qaraqosh two years ago, Father Roni Momika, told Catholic News Agency on Monday that he was hopeful "good news" of his home city would come soon.

It is a "big centre for Christians," he said. Fr Momika was training to be a priest in Qaraqosh when he and his family were forced to flee, so he completed seminary in Lebanon and now works in a camp for the displaced back in Iraq.

He is hopeful of returning home, but returning to Qaraqosh "is very dangerous now because we don't know if our homes and churches have been destroyed or bombed," he said.

"If all is bombed, as it is now in Qaraqosh, they [ISIS] will have destroyed everything," he added. "They will have destroyed our homes, the churches, schools, pharmacies, hospitals.... Please pray for us."