Erbil, Iraq - After the fall of Mosul to the Islamic State-led groups in early June, Michael (not his real name), an Assyrian Christian from Mosul, decided to remain.

Unlike his fellow Christians who left, Michael wanted "to keep an eye on the city's churches." Following the ultimatum, Local church leaders instructed the community members to leave out of fear for their safety.

Fighters led by the Islamic State had made a lightening assault against government forces and took over the city. Mosul is Iraq's second largest city.

Michael described how a statue of the Virgin Mary had been destroyed from outside one of Mosul's churches, and a black flag put in its place. At the time he said he felt like "we are in the quiet before the storm".

On Thursday, that storm arrived when militants issued their decree to the Christians of Mosul.

The last remaining Christians now have fled Mosul after Islamic State militants issued an ultimatum giving them until noon on July 19, the option to convert to Islam, pay a tax, leave, or be killed if they stayed.

The ultimatum triggered a wave of criticism internationally, but also among Muslim scholars.

On Monday, the Secretary-General of the Organization of Islamic Cooperation (OIC), Iyad Ameen Madani, condemned the act against innocent Christian Iraqi citizens in Mosul and Nineveh including forced deportation under the threat of execution.

"This forced displacement is a crime that cannot be tolerated; and the practices of the Islamic State have nothing to do with Islam and its principles that call for justice, fairness, freedom of faith and coexistence," he said in a statement.

In 2003, it was thought that Christians in Mosul numbered 35,000. The number dwindled due to a wave of migration. Some estimates put the most recent numbers at 3,000 Christians out of a city of 2 million people. Before the ultimatum, Michael says only a few hundred Christian families remained in the city.

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"The [religious] tax was in the official letter sent out but we heard from them via our leaders that we could only convert, leave or be killed. Saturday was our last chance."

Michael fled on Thursday evening with three other families crammed into one car - travelling to the city of Dohuk in the relatively stable Kurdistan region.

Getting through the Kurdish checkpoint meant a three-hour agonising wait. "It was not easy, they made it hard for us," he said.

"My family are very sad and crying - we left our land and everything we have so we won't be killed."

At the same time, Christians had their homes marked in red and then confiscated.

Michael is now staying with relatives, but he doesn't know for how long he and his family can remain there or what they will do in the future.

Louis Sako, the Chaldean Catholic Patriarch in Baghdad, warned on Thursday that this "discrimination" will lead to the "elimination of the possibility of coexistence between majorities and minorities".

"Should this direction continue to be pursued, Iraq will come face to face with human, civil, and historic catastrophe."

On Saturday, the prime minister of the Kurdistan Region, Nechirvan Barzani, released a statement calling on the international community to provide aid to those forced to flee, and asking the people of the Kurdistan Region to help the families.

He said that Christian families had come to Kurdistan "without being allowed to take any of their belongings".

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Kurdish checkpoints are currently clogged with internally displaced persons (IDPs) trying to escape Iraq's restive regions. More than 500,000 IDPs have arrived since the fall of Mosul, adding to over 200,000 Syrian refugees already sheltering there.

Mosul has long been an important centre for Christian communities. Not far from the city are the historic monasteries of St Matthew and St Elijah's. But hard times have meant that many Christians have fled Iraq in the years preceding the US-led invasion and in the years afterwards, in the wake of increasing sectarian violence.

In 2010, an attack on the Our Lady of Salvation church in Baghdad killed 58, speeding up the exodus both internally and externally. Many Christians, who at that time fled north, now find themselves under the control of the Islamic State group and are on the move again.

Nadir (not his real name due to security issues) is in late middle age with grown up children. He is part of the Syriac Orthodox church. He studied abroad and has had a long professional career in Mosul. He left with his wife before the ultimatum was issued and now sits in his son's home in a partly finished complex of houses, a few kilometres outside the Kurdish capital, Erbil.

Evening falls as the power fails. We sit in the dark as he takes stock of the situation. "I am the first man ... [to be against] migration from Iraq, but now there is an idea accumulating in my mind to leave," he says, reflecting the feelings of many Christians to whom Al Jazeera spoke. "Everyone is leaving Iraq."

It is not only Christians that are feeling the force of the militants rule, members of other minority groups such as Turkmen, Yazidis and Shabaks have also been captured or killed as the fighting spreads. Shia Muslims remain especially vulnerable to attacks by the Islamic State group.

Air strikes carried out by the Iraqi security forces are adding to the woes of people trapped in fighting zones, many also without reliable water or electricity.

The Kurdish armed forces (Peshmerga) have moved into previously disputed areas of northern Iraq - but in many towns the front lines are not far away.

One Christian resident of Qaragosh, which is under Peshmerga control but saw heavy fighting at the end of June, describes the atmosphere in the town as "a scary kind of safety".

Qaragosh is 30km from Mosul and Archbishop Petros from Mosul's Catholic Syrian church, speaking from Qaragosh, told Al Jazeera that between 200-250 families have arrived in the town since the Islamic State's decree was announced on Thursday. Another resident put the figure as high as 400 families.

"What [Islamic State] is doing in Mosul is not just against Iraqis, it is against all human beings," he said via phone, palpably distressed. "We do not need just letters published to say they are sorry and we are against this or that. This is the time to come to Iraq to stop this - the world should stop this."

"[The Islamic State group] seems intent on wiping out all traces of minority groups from areas it now controls in Iraq," said Sarah Leah Whitson, executive director of the Middle East and North Africa division of Human Rights Watch, in a statement released on Saturday.

"No matter how hard its leaders and fighters try to justify these heinous acts as religious devotion, they amount to nothing less than a reign of terror."

A prominent Muslim leader could not agree more. Sheikh Khalid Al Mulla, head of the Iraqi Scholars Association in the south of the country, in a recent interview, condemned the displacement of Christians from Mosul and accused the Islamic State of "falsely wearing the dress of Islam to displace the Christian brothers who live with us for thousands of years".

"Religious scholars should take responsibility in upholding the true voice of Islam," he said.

