Latest reports received by Aid to the Church in Need, the charity for persecuted and other suffering Christians, indicate an increasing state of alarm with Christians now being shot dead at an average rate of two a day as Islamic militants assert their authority over the city.
The latest victim in a killing spree which has claimed the lives of at least 15 Christians is 38-year-old Jalal Moussa, who reports state was shot dead outside his home on Wednesday.
Sources close to the scene report that another two Christians may also have been killed in the incident in Mosul's Noor district.
Preparations are underway to help Christians fleeing the city with emergency food, medicine and shelter which is being stockpiled in neighbouring villages including the Christian town of Qaraqosh where security is much better.
Speaking from Erbil, in Kurdish-controlled northern Iraq, Father Bashar Warda, from the Chaldean Catholic Church, told ACN: "We are afraid that that what is happening in Mosul will develop into a massacre."
Archbishop Louis Sako of Kirkuk, who has nominal oversight over Mosul after the death of Archbishop Paulos Faraj Rahho who was kidnapped in February 2008, added: "I am very worried. The situation is now critical."
The archbishop has sent a message pleading with the fanatics to stop the violence.
