Baghdad, Iraq (CNN) - Just days after the militant group the Islamic State in Iraq and Syria said they killed hundreds of Syrians, dozens of Iraqi Christian families are now fleeing the ISIS-controlled city of Mosul, hoping to avoid a similar fate.

On Friday, the al Qaeda splinter group issued an ultimatum to Iraqi Christians living in Mosul - by Saturday they must convert to Islam, pay a fine or face "death by the sword."

A total of 52 Christian families left the city of Mosul early Saturday morning, with an armed group prohibiting some of them from taking anything but the clothes on their backs.

"They told us, 'You to leave all of your money, gold, jewelry and go out with only the clothes on you,'" Wadie Salim told CNN.

Images obtained exclusively by CNN show that the phrase "property of ISIS" scrawled in black paint on a number of the homes that were abandoned.

Some of the families headed for Irbil - which is currently controlled by Kurdish forces - and others toward the Dohuk province. The majority went to Dohuk, which is 140 kilometers (87 miles) north of Mosul.

"We did not know how to act," said another Mosul resident, Um Nazik. "Are we going to get killed?"

ISIS was able to take over large swaths of land due to the lack of centralized authority in both Iraq and war-torn Syria. The Sunni militants hope to establish an Islamic state throughout the region it currently controls.