The Iraqi army offensive to retake Mosul from Islamic state began two weeks ago. More than 18,000 civilians have escaped from towns in the region but it is believed that 1.5 million people are still unable to find a safe route out of the city.
Francis Guy, Christian Aid's Head of Region for the Middle East said: "The liberation of Christian, Shabak and Turkmen towns highlights the multi-religious make up of Iraq. The opportunity to rebuild a lost harmony must not be thrown away in a potential rush for revenge.
"Civilians are caught in the middle of an increasingly complicated conflict with different forces on all sides of the city and little concern for humanitarian principles."
A spokesperson for a Christian Aid partner organisation based in Iraq has described the situation in Mosul as alarming; "[Civilians] are terrified of the shelling, they are trapped at home, they cannot leave the city because of ISIS [Islamic State]."
Mosul was once a centre for trade and melting pot of cultures in Iraq, however that changed when the city was captured by ISIS two years ago.
- Population pre-2014: around 700,000 people
- Tens of thousands have fled since 2014
- Red Cross says up to a million people are homeless
The terrorist group inflicted high tax on the city's citizens, causing many families to starve.
Hundreds of thousands of Christians have been forced to flee the region since 2014 and those that stayed faced death, torture and slavery.
On Sunday, the first Catholic Mass in two years was held at a church in the nearby town of Qaraqosh.
Islamic State released audio tape on Thursday in which the leaders said they had no plans to surrender control of Mosul.