Father Daniel said the death cult still exists in the minds of people brainwashed while living under their rule in Iraq and Syria.
The priest told Express.co.uk those who were forced to live under ISIS rule in towns and cities controlled by the group had succumbed to their propaganda and continue to support their extremist views today.
Father Daniel said: “ISIS has been defeated only militarily. Mentally, it still exists under many people who lived under their control.
“For an example, Mosul. Two million people lived there. They ran schools so of course this is going to effect the minds of the students.
“Everything should be according to their faith and their thinking. If you are against their thinking you will be ex-communicated or killed.”
Christians living in towns controlled by ISIS were given an unenviable choice between paying off fighters, converting – or facing death.
He said: “Anyone who stayed under ISIS control had two options: to pay very high taxes or to convert to Islam. That is the safe option.
“If you didn’t pay or convert you would be executed in public.”
Father Daniel himself was forced to flee extremism as a teenager due to the threat of Al Qaeda.
His father was also a priest and this role put his family, based inn Baghdad, in danger during a wave of extremism in the early 2000s.
Father Daniel said: “The situation went from bad to worse. After that the Christians became targets for radical groups. They took advantage of the weak government.
“They started to blackmail people, sending killing threats to Christians because of our faith and belief.
“My father is a priest so we got killing threats. They said we had leave in 24 hours or we would be killed. We left in the early morning.
“I was 16 – it was on the day of my sixteenth birthday. My gift that day was crying all the way because I was leaving my school, my friends, my church behind. That was very hard for me.”
Father Daniel and his family fled to the town of Erbil. He believes his presence in the city was no coincidence.
Several years later the town would be flooded with Iraqi families fleeing the new threat of ISIS. Since then Father Daniel has worked with and helped these refugees, who he prefers to call “relatives – because we are all family”.
He said: “I was one of the first ones who received the displaced people. I believe God had a plan. “