23 Christian families are stranded in the ISIS-controlled city of Raqqa

Militant Islamist fighters take part in a military parade along the streets of northern Raqqa province, June 30, 2014.REUTERS/Stringer

The Islamic State (IS) is forcing the 23 remaining Christian families in Raqqa to pay jizya or a "protection tax," Agenzia Fides reported Saturday.

Beginning on Sunday, the families were expected to pay the equivalent of $535, or be expelled from their homes.

There were once 1,500 Christian families in the northern Syrian city, but nearly all of them have fled since IS took over the city in August. US airstrikes in the area also caused Raqqa residents to flee.

"After the air strikes started, people got scared," a Raqqa resident using the alias Abo Ward Al-Raqqawi told Radio Free Europe Radio Liberty. "Some people escaped to Turkey or Damascus or to other government-controlled areas.

"In Raqqa, everyone is afraid of the air strikes. Raqqa is like a ghost town."

The Christians that remain are unable to leave the city due to their age, health, or lack of resources, and face relentless persecution. Residents leave their homes for only a few hours each morning to gather food and other items, and the schools are closed. There is also the threat of death.

"The executions are a little bit less now, because there are fewer people to be executed," Raqqawi said. "But last Friday they executed two people here in the public square."

The main Armenian church in Raqqa was turned into an IS office, and the militants burned Bibles and other Christian materials.

Raqqawi fears that there is no stopping the terrorist group, and blames the US and its allies for not reinforcing the Free Syrian Army (FSA).

"Now IS is so strong. It controls Raqqa and soon it will control many more cities in Syria," the activist insisted. "IS will grow stronger. Then there will be a real risk that no one will be able to fight them.

"If the United States had given the FSA weapons, then they would have been able to kick IS out of the city," he continued. "IS would not have taken over. The Americans and the international community said they would give weapons but it was all lies. Just talk, talk, talk."