Syrian rebel group Jaysh al-Islam has executed 18 alleged members of Islamic State (Isis) in a gruesome video that imitates the ones produced by the rival extremist group.

The footage shows fighters from the anti-Assad group, which rejected membership of the Western-backed Free Syrian Army, wearing the orange prison clothes of the IS victims – while the IS members are dressed in black and chained together. The prisoners are also wearing ankle and hand shackles with metal balls attached.

Further to the reverse colour scheme, sophisticated sound effects and visuals are similar to those featured in IS execution videos, as well as quotes from Islamic texts:

Jaysh al Islam speaker in Ghouta is also quoting the same verse from Surat al Tawbah quoted in many videos released by the Islamic State — Daniele Raineri (@DanieleRaineri) July 1, 2015

Fighters for Jaysh al-Islam – which is a joint force created by the al-Qaeda-linked al-Nusra front and Ahrar al-Sham, another Islamist rebel group – say in the video that the IS members are being executed as revenge for the beheading of three of the rebel group's members.

Jaysh al-Islam, which has fast become one of the most successful actors in the Syrian war, is based in Ghouta, in the outskirts of Damascus. It accused IS of being allied with the Assad regime against its fighters.

It claimed that IS is betraying Sunni Muslims and joining forces with Shi'ite Muslims and "Nusayris", a derogatory terms for Assad's Shi'ite offshoot of the Alawite sect.

The video also features confessions from IS fighters, who admitted not fighting against the Syrian army. At the end of the clip, 18 men are forced to kneel before Jaysh al-Islam fighters, who then shoot them in the head.

Just like in IS videos, the shots are filmed from different angles and with close-up shots.