Hundreds have found shelter in areas between Mosul and Irbil that are controlled by Kurdish Peshmerga fighters

Iraqi Christians who were forced to flee the northern city of Mosul under threat of forced conversion or execution by jihadists have spoken of their terror as churches were turned into mosques and their homes and property confiscated.

The expulsion of one of the world's oldest Christian communities provoked condemnation and anguish from figures as diverse as the pope and Iraq's prime minister, Nouri al-Maliki, who lambasted the Islamic State (Isis) for its "criminality and terrorism".

Last weekend Isis gave the city's Christians a stark choice: convert to Islam, pay a religious tax, or face death. "They said there is no place for Christians in the Islamic state," one distraught refugee said from the safety of Bashiqa, 16 miles from Mosul. "Either you become Muslim or you leave." Mosul's last 1,500 Christian families were reportedly robbed at Isis checkpoints as they fled.

Hundreds have found shelter in areas between Mosul and Irbil – the capital of the Kurdistan regional government – that are controlled by Kurdish Peshmerga fighters, but they face an uncertain future.

"If Isis stays, there is no way the Christians can return," Father Boutrous Moshi said from Qara Qoosh, a Christian area south-east of Mosul. "It is up to God whether we return or not. They have not burned the churches but they did set fire to the pictures and the books and broke the windows."

Monks at the 4th-century Mar Behnam monastery, a major pilgrimage site run by the Syriac Catholic church, were allowed to take only the clothes they were wearing.

Sarab Hazem, from the Zehoor neighbourhood of Mosul, said that initially there were no attacks on Christians when Isis took the city in a lightning offensive in June, though Isis fighters did capture and take away police, security agents and soldiers. "No one knows what becomes of them," he said.

Then, statues of Christ and the Virgin Mary were destroyed. "They are savages," Hazem said. "This is oppression for no reason. I believe it is no longer possible for Christians to live in Iraq."

Bashar Nasih Behnam, 52, who fled with his two young children last Friday, told a similar story: "They [Isis] threatened us and said you can't stay in Mosul and you have to leave," he said. "They said we have conditions: either you comply with them or you leave. So we left."

Deprived by Isis of Iraqi government rations (a legacy of the sanctions imposed in the Saddam Hussein era) they were too frightened to go out to their church, where the jihadis took down a statue of the Virgin Mary and put their black flag in its place. A monastery was turned into a mosque.

Two nuns who were looking after three orphans were kidnapped but later released. The Arabic letter "N" for Nasrani (Christians) was daubed on the doors of houses – to show that they had been seized as the property of the Islamic state declared by Isis.

"There is not a single Christian family left in Mosul," Behnam said. "The last one was a disabled Christian woman. She stayed because she could not get out. They came to her and said you have to get out and if you don't we will cut off your head with a sword. That was the last family.

"There is not a single family that left and was not robbed. They took our money, gold, even the earrings from their [women's] ears. They took everything, even mobile phones.

"We don't know if we are going to go back. Until now we have no idea if there can be a return. We don't know what our destiny is. They have even taken our houses in Mosul."

Bassem Fadel Zarghit, a shopkeeper from Mosul's al-Rifa'i neighbourhood, said the city's Christians had felt doomed despite initial reassurance from Isis. "There is no one left," he said. "It's not just the Christians. It's also the Shia that are being targeted."

Mosul, the largest city in northern Iraq, was once among the country's most mixed. Waves of attacks on Christians since the 2003 US-led invasion to topple Saddam have eroded its once sizeable Christian population, mainly from the Assyrian and Chaldean denominations.

The decree issued by Isis in Mosul mirrored one that its fighters issued in the north-eastern Syrian city of Raqqa in February, demanding that Christians pay the jizya levy in gold and curb displays of their faith in return for protection.

Human Rights Watch has condemned Isis for its vicious campaign against minorities in the Mosul area.