THe extremist Islamic State has released one of its most brutal videos to date, showing prisoners drowned, blown-up with explosives and shot with a rocket-propelled grenade (RPG).

The video was filmed in Iraq's northern Ninawa province near Mosul, according to Site Intelligence, a global jihadi monitoring agency which has published images from the video. But it remains unclear where and when the video was shot. The seven minute video, released on Tuesday, appears to be filmed by HD cameras.

The sixteen Iraqi prisoners are accused by the Islamic State group, refer as ISIS/ISIL or Daesh in Arabic, of being spies, reported CNN. The jihadists also recorded the accused men's confessions before executing them by different methods.

Images from the video showed five men dressed in orange jumpsuits locked in large metal cage. The cage was then lowered into a swimming pool with underwater cameras which filmed the men drowning. Afterwards the cage lifted back with dead bodies piled on top of one another.

Four other prisoners were blown up using a rocket-propelled grenade, according to AFP. They were locked in a car that was blown up by an RPG. A third group consisted of of seven prisoners who were beheaded with explosive cords wrapped around their necks. The video concluded with horrifying close ups of the victims' dead bodies. The terror outfit did not reveal identities of victims.

"Essentially, a lot of these execution videos, which are far more gruesome than the early executions and are often public spectacles, try to demonstrate that the local population will not have a life outside of ISIS. It shows them that if you try to collaborate with the Iraqi regime, they will kill you in a fashion like this," Benjamin Decker of the Levantine Group commented on video, according to Newsweek.