A survivor of the Islamic State (ISIS) rampage in Iraq has provided a fresh account of a Christian man's horrific crucifixion by the Islamist extremists.

The survivor identified only as Esam told the persecution watchdog World Watch Monitor that ISIS militants brutally crucified his brother-in-law "like Jesus" and forced his wife and children to watch.

"My wife's brother was crucified by Daesh," Esam said, using another name for ISIS. "He was crucified and tortured in front of his wife and children, who were forced to watch. They told him that if he loved Jesus that much, he would die like Jesus."

Esam said the militants tortured his brother-in-law for five hours—6 p.m. up to 11 p.m. They then crucified him, cut his stomach open and shot him, he added.

Last year, the Virginia-based Christian Aid Mission reported that ISIS heinously tortured and killed a 12-year-old boy, along with 11 local Christian missionaries, after they refused to leave their homeland or renounce Christ, the Gospel Herald reported.

"All were badly brutalized and then crucified," an indigenous ministry leader told the outlet. "They were left on their crosses for two days. No one was allowed to remove them."

Esam said two other members of his wife's family, a Christian couple, were also abducted by ISIS. To this day, the husband has not been heard of since and the wife "now lives with one of the Daesh amirs," he said.

The survivor also revealed that Christian girls from his hometown were taken as sex slaves by the ISIS militants. "We heard of 12 Christian girls who are with Daesh," he said. "They may be more. Our bishop told people not to tell if they lose their girls" because "it is a shame on the family."

ISIS militants have been killing and brutalising Christians and other minorities since 2014 when they managed to grab territories belonging to Iraq and Syria. This has decimated the Christian population in the conquered areas. For instance, a decade ago, 35,000 Christians lived in Mosul. Now, only 20 or 30 remain, according to the Gospel Herald.

Esam said some of the damages done by ISIS have already been reversed and that some of his friends who escaped Mosul in 2014 after being forcibly converted to Islam have been "baptised back to Christianity."

Still, despite the liberation of villages around Mosul, many Christians who have left the city are not eager to return home soon because of the destruction of their homes, their mistrust of Iraq's security forces and their fear that the Sunni Muslims in their area collaborated with ISIS and could once again target them for persecution, sources said.