Iraq's Christians no longer see the Nineveh Plains as the safe heaven they once were, according to the governor of Mosul's former advisor on Christian affairs.

ISIS militants captured swathes of Nineveh province in 2014 and obliged its Christian population to convert to Islam, pay a religious tax, or leave Mosul. The majority opted for the third choice, although they didn't escape ISIS rule unharmed.

Related: Timeline of ISIS in Iraq
Related: Attacks on Assyrians in Syria By ISIS and Other Muslim Groups

"ISIS militants destroyed thousands of Christian houses in the province of Mosul and ruined 120 churches and Christian shrines," said Durayed Hikmat, who advised the governor of Mosul on Christian affairs for eight years.

The renovation of these properties will cost more than 15 billion dinars, Hikmat estimated.

"ISIS militants kidnapped more than 100 Christians in the Hamdanya area when they came to Mosul and its surrounding areas -- only 20 of them escaped, 55 were killed, and the fate of 25 more is unknown," Hikmat said.

"Some of the Christians who were captured were women," he added.

"After ISIS was defeated, we tried to get some information about them. Some of them were sent to Syria and we think they are still there."

According to unofficial figures, there were as many as 1.5 million Christians in Iraq in 1980s, mostly living in Baghdad, Mosul, Duhok, Erbil, Kirkuk, and Basra. But their number has been dwindling in recent years owing to consecutive conflicts. Many of them emigrated to Europe and North America.

According to these figures, there currently are 250,000 to 300,000 Christians remaining in Iraq -- the majority living in the Kurdistan Region.

"Mosul is an important city to Christians where there are many Christian archeological sites. But ISIS destroyed most of them," Hikmat said.

"Half of the number of Christian IDPs in the Kurdistan Region have decided not to return to Mosul. They have found jobs here and sent their children to Kurdistan schools," he said.

"So far, 16,000 Christian families have returned, mostly returning to Hamdanya. Only 40 families returned to the city of Mosul, who later returned to the Kurdistan Region because of the hardship they faced upon their return," Hikmat added.

Many don't believe it is safe to return.

"The Hashd al-Shaabi forces on the Nineveh Plains are making trouble for the return of IDPs to their places. They try to turn the people of the area into Shiites, seize the properties of Christian people, change their notaries and sell them. That is why Christians are afraid and don't feel passionate about returning to their places," Hikmat said.

He goes as far as to suggest there is a regional plot to cleanse the Middle East of its Christian population.

"There has been a regional plot for 10 years against Christians in the Middle East, Iraq, Syria, Lebanon, and Egypt. The life of Christian people is in danger and we have informed the international community of this danger. The US and France especially are making efforts to protect the Christian population in the Middle East," Hikmat said.

"Throughout the Middle East, only the Christians living in the Kurdistan Region feel safe," he added.

Hashd al-Shaabi has formed a Christian force called the Babilyon regiment on the Nineveh Plains to defend local Christians. The head of the force is a Christian called Rayan Kildani. However, many in the community do not feel the force represents them.