London: Islamic State (IS) terrorists in Syria have released a video of beheading 12 men, accused of fighting for the rival terror groups Al Qaeda and Jaish al-Islam, media reported on Friday.

Filmed in Syrian capital Damascus, the footage shows 12 men being interviewed and paraded in front of the camera before the execution on Thursday, a report in London-based Daily Mail said.

After "confessing" to the crime of opposing IS and failing to declare allegiance to the terror group's leader Abu Bakr al-Baghdadi, every terrorist was executed by a different masked member of the Islamic State group.

The video — titled "Repent Before Being Overcome" — bore all the high-tech hallmarks of the terror group that other murder videos earlier have had.

In a slick bit of editing before the executions, the footage momentarily rewinds and fades into a montage of Al Qaeda and Jaish al-Islam fighters battling IS, the report said.

The overall theme of the video is along the same lines, and sends a clear signal to other terrorist groups fighting in Syria that they must declare allegiance to IS "before being overcome", report added.

While speaking directly in front of the camera, the men appeared clean-shaven a rarity for terrorists and something likely to have been intended to humiliate the men before they were killed.

Earlier, a footage was released that showed IS terrorists executing 16 Iraqi nationals on charges of "spying" for coalition forces. (IANS)