Christians in Raqqa in Syria are being prevented from leaving and instead are being forced to study Islamist teachings such as jihad, according to activists in the city.
Raqqa is Being Slaughtered Silently, the Syrian Campaign Against Islamic State and also the Assad regime, tweeted:
The group also tweeted:
In addition, Raqqa is Being Slaugtered Silently tweeted examples of Islamic State propaganda urging followers to follow the examples of the terrorists who bombed Belgium and do the same in countries such as Germany.
The group estimates there are 43 Christian families with two or three people in each remaining in Raqqa. They have survived so far by paying a tax and agreeing to follow Sharia law. In addition, they are being protected from extremists by their Muslim neighbours.
Muslims also are being prevented from fleeing, whether they support Islamic State or not.
The ISIS crackdowns on residents remaining in Raqqa, the headquarters of the so-called caliphate, came as Syrian government forces backed by heavy Russian air support drove Islamic State out of Palmyra on Sunday.
The loss of Palmyra, where some of the world's most important heritage sites were destroyed, came as a big setback for Islamic State.
Palmyra was recaptured with help from Russian and Syrian air strikes.
The victory meant the desert roads leading east towards Raqqa and the other main Islamic State stronghold, Deir al-Zor, are now open.