Isis child executioner
A child executioner for Isis is seen shooting several prisoners in Tikrit, Iraq.Screenshot

Horrifying new Isis propaganda footage features a child executioner shooting prisoners in the back of the head on the banks of the Tigris River in Iraq.

According to the Daily Mail, the footage was filed during the Isis mass killing spree in Tikrit in 2014. The child executioner, a young boy, is seen shooting two men in the head with a pistol, ignoring the men's desperate pleas for mercy. The victim's bodies are then thrown into the river, which turns red with their blood.

The terrorist group's new video also shows scores of young men pleading for their lives before they are put in shallow graves and showered with bullets. Other victims in the video are executed individually, the Daily Mail reported.

The footage of the boy executioner is part of a longer, equally graphic 22-minute-long video released by Isis over the weekend. The video was filmed amid one of the largest Isis-led massacres, at the Speicher military base, which left an estimated 1,700 dead.

At one point in the propaganda video, an unnamed Isis militant clad in a military uniform, speaking directly to the camera says, "This is a message I address to the whole world and especially to the Rafidha dogs, I tell them we are coming." The term "Rafidha dogs" is a pejorative term used by Isis to refer to Shiite Muslims.

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Isis fighters murdered such a vast number of Iraqi cadets that the victim's graves could be seen from space using satellite imaging. Nearly 600 bodies have been exhumed since Tikrit was recaptured from Isis in April.

The massive killing, along with a call to action by Iraq's leading Shiite cleric Grand Ayatollah Ali al-Sistani, has led to the mass recruitment of Shiite volunteers to fight against the terror group.