Islamic State (IS) fighters have killed 85 civilians and abducted 400 more in eastern Syria, a monitoring group has claimed.

The Syrian Observatory for Human Rights said on Monday it feared the abductees taken from al-Baghaliyeh village outside Deir al-Zour city would be killed or forced to become slaves. They were mostly the wives and children of Syrian army soldiers, the group said.

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“We fear that the 400 will be executed or enslaved by the organisation on the pretext that they are loyal to the regime,” Observatory head Rami Abdel-Rahman told local media.

Syria’s government-controlled news agency reportedly estimated the civilian death toll much higher at 300.

The village was seized by IS during the attack, and the captives reportedly taken to nearby areas of Syria also under the group’s control.

The Syrian army is reportedly mustering to retake the village.

Women are routinely subjected to sexual slavery in Islamic State-held territories. The group recently issued a fatwa, or religious order, setting out the ‘acceptable’ ways in which female victims may be raped and sold.

-with AAP