Less than one quarter of the former Christian population has remained, the bishop told AsiaNews.
"Threats, sanctions, discrimination, blackmail, Islamic propaganda in the schools, slogans on the walls, have driven even the moderate Muslims to stop defending their Christian brothers from intolerance," he said.
"Once they used to open their homes to the Christians; now, out of fear of fanaticism and terrorism, they do not even dare show that they are friends or acquaintances of Christians.
Earlier, The Age reported that after a series of atrocities against Iraqi Christians in Mosul, around 400 Christians arrived in Syria to escape the harsh conditions of home, according to a statement by a Syrian refugee assistance organisation.
In the last few days, some 20 Christian families arrived in the city of Qamhley, which is close to the Syrian-Iraqi border, said Lauren Gul, a representative of the refugee assistance group.
Since the end of September, Iraqi Christians in Mosul, which lies 405 kilometres north of Baghdad, have been targeted by extremists.
Hundreds have been killed, while the rest have received death threats. Most have sought protection in surrounding villages.
The UNHCR is currently assisting hundreds of Iraqi Christians who fled from Mosul to Syria. Most of them asserted that they would return home soon.
Meanwhile, Christian MPs condemned the Iraq security forces for failing to protect Mosul's Christians.
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