The handful of Christian families remaining in ISIS' Syrian stronghold of Raqqa have been forbidden from fleeing the city, according to a tweet from a secret group that reports from inside the caliphate.

The activist group Raqqa is Being Silently Slaughtered said the black-clad terrorist army issued a decree that any Christians or Armenians still within city limits may not leave. It is believed that there are just more than 40 Christian families left in the city, and that they have been forced to register with the extremist group and to pay a "jizya," or a minority tax in exchange for being unharmed.

"Any Christian living within Syria or Iraq is in a very dangerous and precarious position,” David Curry, president and CEO of Open Doors USA, a Christian advocacy organization, told FoxNews.com. ‘We want to see the Christian church survive in the Middle East, especially in the areas occupied by the Islamic State.”

“Any Christian living within Syria or Iraq is in a very dangerous and precarious position.”

- David Curry, Open Doors USA

Raqqa first fell into rebel control in March 2013 after a battle between Al Qaeda-linked jihadi group Al Nusra and Syrian President Bashar Al Assad’s regime, becoming the first provincial capital under rebel control. ISIS has since used the city as a launching point to increase their caliphate.

According to Raqqa is Being Silently Slaughtered, there are about 43 Christian families left in the city.

“The suffering of Christians began with ISIS control of Raqqa,” RIBSS said on its website, according to news blog The Foreign Desk. “ISIS looks at Christians as infidels loyal to the West more than their loyalty to their homeland which they live.”

Sources in contact with people in Raqqa told FoxNews.com that the ban extends to all citizens within the city.

Christians once accounted for up to 20 percent of the population in Syria, but recently, that number has been dwindled to 10 percent.

Islamic extremism and authoritarian governments combined to make last year the worst in modern history for Christians around the world, according to a recent report from Open Doors USA. The trend spiked upward in the Middle East, Africa and Central Asia, with thousands of Christians killed or imprisoned, and even more chased from their homes. ISIS alone is responsible for driving out the entire Christian population in Mosul, long considered a Christian enclave in Iraq’s Nineveh Plain.

Two weeks ago, the U.S. State Department officially declared a “genocide” designation in regards to the treatment of religious minorities in Syria and Iraq.

"This is another chapter in the sad story of genocide in the region against Christians, apostates and other minorities,” Ryan Mauro, national security analyst with The Clarion Project, told FoxNews.com.

In 2014, as they gained a foothold in the region, ISIS established a list of restrictions that Christians living in Raqqa had to follow in order to live under the Caliphate. In addition to registering and paying extra tax, they are banned from building or repairing churches, displaying Christian symbols and praying in public.

Perry Chiaramonte is a reporter for FoxNews.com. Follow him on Twitter at @perrych