The Syrian opposition Observatory for Human Rights said the spike in execution-style killings follows the killing of 10 ISIL gunmen in hit-and-run attacks in several areas around Deir Ezzor province this month.
Deir Ezzor stretches from Raqqa to the border with Iraq and links ISIL's self-declared caliphate in the two countries.
Syrian state news agency SANA said on Thursday ISIL executed three civilians and displayed their bodies in the town of al-Mayadin.