The Syrian opposition group, Jaysh al-Islam has executed 18 alleged Islamic State militants. A video emerged of the rebel organization imitating many of the jihadist group’s own execution recordings, including similar sound effects and visuals.

The clip, which was just under 20 minutes long, showed fighters from Jaysh al-Islam (Army of Islam) wearing orange prison attire, that victims of Islamic State (IS, formerly ISIS) are often executed in.

However, the ‘executed’ became the ‘executioners,’ as they slayed 18 prisoners, who were dressed in black cloths, reminiscent of IS’s main dress style.

The slick production, with numerous computer graphics and special effects included, showed the IS prisoners being marched in unison, and chained together at the neck and at their hands.

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The alleged members of IS were then forced to kneel in a long line and were executed with a bullet to the head. The shots were filmed from numerous angles and also included some gruesome close-ups.

The captives were killed partly in revenge for the deaths of at least of three of the rebel group’s members, who were beheaded by the jihadist terrorist organization last week, AFP reports.

The video also included numerous use of sectarian language, while it also accused the group of betraying Sunni Muslims and allying with Shiite Muslims and “Nusayris,” which is a derogatory term for the Alawite sect, to which the Syrian President Bashar Assad belongs.

Interrogations that appear during the video also show apparent confessions from the prisoners that IS had concentrated mainly on fighting against other opposition groups, rather than on fighting against troops loyal to Assad.

Two months ago, Jaysh al-Islam released another video, this time showing a military parade, featuring 1,700 troops and numerous tanks. Dozens of fighters showed off their skills in close combat, in what the group called, the “largest military parade witnessed,” since 2011, when the civil war started. The group has a stronghold in the eastern Ghouta region on the outskirts of the Syrian capital, Damascus.

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Overall, Jaysh al-Islam, which is made up of over 50 different factions, has as many as 25,000 loyal fighters. It has received financial backing from the Gulf States.

Jaysh al-Islam also launched a major offensive against the Syrian capital in February. They launched at least 40 rockets at homes, reportedly leaving dozens of civilians wounded and at least three dead.

The Russian embassy in Damascus was damaged in militant attacks on February 5, with several shells exploding near its territory. None of the staff was injured.