The Daesh militant on Monday killed at least 16 civilians at their base in Deir ez-Zor, the largest city in Syria, Syrian Observatory Human Rights said to reporters.
The Syrian Observatory Human Right added that half of the victims are Syrian children.
It comes after when Syrian forces, under leadership of the United State Coalition, starts operation against the remaining Daesh militants in the northeast part of the country.
Sources said Syrian forces succeeded in eliminating terrorists in their final operation, in which they seized at least 41 Daesh bases in the country.
According to Syrian forces, more than 500 Daesh militants and about a 1000 civilians are sieged in areas where battle between the insurgent and forces is ongoing.
