Syrian Observatory for Human Rights said on Wednesday that Islamic State group (ISIS) terrorists had executed nearly 700 prisoners in nearly two months in eastern Syria.
The UK-based war monitoring group said the prisoners were among 1,350 civilians and fighters that Islamic State had been holding in territory near the Iraqi border.
The jihadists control a shrinking strip of land east of the Syria's Euphrates River around the town of Hajin, which US-backed forces entered this month.