The killings followed the arrest of 35 members on Saturday, April 2 in Raqqah.
It is reported by a western news agency citing the Syrian Observatory for Human Rights that ISIS killed 15 of its members in the largest execution of the militant group’s security services so far in Syria.
According to the Britain Based SOHR that claims of monitoring the five-year-old Syrian conflict through a network of sources on the ground, the killings followed the arrest of 35 members on Saturday, April 2 in Raqqah.
It also said that the members were killed in connection with the assassination of senior Islamic State figure Abu Hija al-Tunisi, who died on Wednesday in an air strike.
Abu al-Haija al-Tunusi was allegedly sent by Abu Bakr al-Baghdadi, the leader of the ISIS to oversee the military operations of the organization in the northeastern countryside of Aleppo. Due to the drone strike, another IS member accompanying Tunusi in the vehicle was also killed.
Recently, the Syrian army backed by Russian airpower liberated Palmyra from the ISIS terrorists.
Russia said that it has conducted more than 500 sorties to destroy 2000 ISIS targets in just 20 days of March.
A truce agreement was negotiated by Russia and the United States regarding Syrian conflict although many analysts suggested that the Washington had been supporting terrorists fighting against the Syrian government forces.
Nevertheless, the Arab country is currently observing an agreement for the cessation of hostilities which entered into force on February 27. The agreement stipulates the cessation of all military hostilities in Syria, except for the operations against ISIS terrorist group and al-Qaeda-linked al-Nusra Front militants. From the middle of the March, Russia has been partially withdrawing troops and warplanes from Syria to make an end to the Syrian crisis.