Islamic State jihadists have begun closing in on two cities in northern Syria where there are still significant Christian communities.

“IS is attacking Hassaka, and the situation is not that secure,” Father Emanuel Youkhana from the Christian Aid Program in Northern Iraq (CAPNI) told the Catholic Aleteia network on June 4. “IS can advance probably, as the Arab Sunni tribes may join and help IS.”

By taking over a major power plant at the southern edge of Hassaka City, the militants “seem in a position to control the daily life of people in Hassaka,”a local source told ARA News. According to the independent Syrian press agency, large numbers of the Arab and Christian residents have fled to districts north of the city.

Hundreds of Hassaka province’s Assyrian Christian families were forcibly displaced by an IS invasion of their villages along the Khabur river in late February. The fate of more than 230 Christians who were taken hostage during the offensive remains unknown.

At the same time, the IS militants are escalating their longstanding attempt to seize control of Aleppo, Syria’s largest city, which controls the insurgents’ strategic supply route to Turkey. Estimated at more than 100,000 in the early years of the Syrian civil war, the historic Christian population of Aleppo has since been decimated by targeted violence against Christian civilians, including the kidnapping and murder of church leaders, which has pushed many to flee the country.