A rival jihadist group in Syria has apparently turned the tables on the Islamic State as the latter's captured fighters are shown being executed by the group's own fighters wearing orange jumpsuits—the trademark attire worn by prisoners executed by ISIS militants.

In a 19-minute video similar to those released by ISIS to show its brutal executions, the group called Jaysh Al-Islam, or the "Army of Islam," is shown leading 13 alleged ISIS fighters wearing black clothes and masks to their deaths, The Daily Mail wrote.

The video shows the 13 ISIS prisoners wearing shackles. A Jaysh Al-Islam commander orders them to kneel and then speaks: "Allah did not make a disease without appointing a remedy to it."

A Jaysh Al-Islam fighter then speaks: "The most serious calamity for our jihad today is a group of people who grow at a time of division among Muslims. This group claimed to be the mother state and made Takfir [accused of apostasy] on other Muslims, shed their blood and looted their properties and dignities.

"They worsened... the ordeal of Muslims by corrupting their religion and livelihood and killing the jihadi leaders who did their best to help our stricken nation.

"They wreaked havoc on our people in liberated areas and cut the supply route of jihadis. They left... Tehran intact and instead they attacked our mosques.

"This is the penalty for what they have committed. We also call on their fellows to repent."

The ISIS prisoners are then unmasked and made to drink something as the camera focuses on each of their faces. They are then shot at the back of their head at point-blank range with shotguns.

Jaysh Al-Islam reportedly commands as many as 25,000 fighters after around 60 rebel factions in war-torn Syria merged in 2011.

The group released a video in April showing its 1,700-strong soldiers as well as a fleet of armored tanks.

It operates in the Syrian city of Damascus, with Saudi Arabia reportedly investing millions of dollars to arm and train its fighters.

The group, led by Sheikh Zahran Aloush, is reportedly being backed by the Arab kingdom in a bid to defeat the Syrian regime and increasingly powerful jihadi groups like the Al-Qaeda and ISIS.