A Syrian rebel group has executed 18 alleged members of Islamic State (IS) in a video mimicking the extremist organisation's own productions.

The video shows fighters from Jaysh al-Islam (Army of Islam) wearing the orange prison clothes that IS victims often sport.

The IS prisoners, however, are wearing black clothes and are chained together wearing ankle and hand shackles with metal balls attached.

The nearly 20-minute production mimics many aspects of IS's own execution videos, with similar sound effects and visuals.

Jaysh al-Islam fighters in the video said the IS forces were being executed in part as revenge for the deaths of at least three of the rebel group's members, who were beheaded by IS.

The rebel group also refers to a major battle it fought with IS in February.

It accuses IS of being allied with Syrian president Bashar al-Assad's regime against its fighters and those of other Islamist rebel groups.

Video intended as payback for executions

The video includes starkly sectarian language, accusing IS of betraying Sunni Muslims and allying with Shiite Muslims and "Nusayris", a derogatory terms for the Alawite sect to which Mr Assad belongs.

It contains lengthy "confessions" from IS fighters who claim they did not fight against the Syrian army while with IS.

The interrogations appear intended to show that IS has focused its fight on other opposition forces, rather than the Syrian government.

The last part of the video shows the 18 IS fighters in black, kneeling before Jaysh al-Islam executioners who shoot them in the head.

The IS group emerged in Syria in 2013, when it sought to merge with Al Qaeda's local affiliate, the Al Nusra Front.

But Al Nusra refused the merger, and IS has since been at odds with the group as well as Islamist and moderate rebels.

In the area around Damascus, its forces have battled Jaysh al-Islam and other rebel organisations.

Last week, a video emerged showing IS jihadists beheading 12 men from rival groups, among them at least three from Jaysh al-Islam and one from Al Nusra.

AFP