More evidence that children are being indoctrinated and trained to become jihadists in territories controlled by the Islamic State (Isis) group has emerged in the form of a video showing a little boy learning to shoot and kill.

A child, looking as young as five, is seen firing a pellet gun as he re-enacts a combat scenario running through the streets of a Syrian city, in footage posted online by an activist group.

The blonde-haired boy takes cover behind walls and pauses to reload his weapon acting like an experienced fighter, while another two children and a suspect militant look on.

The video was posted online by Raqqa is Being Slaughtered Silently - a small activist collective which secretly documents the shocking violence and oppression inflicted by the IS on their home city.

"This video is yet more evidence of Islamic State seeking to indoctrinate children from a very young age in an attempt to entrench its hold over the region," Charlie Winter, a spokesman for the London-based Counter-extremism Quilliam Foundation Think Tank, told the MailOnline.

"Such footage is worrying; in particular because it renders apparent the fact that IS' legacy will be long-term, even if it was to collapse tomorrow."

Raqqa, in northeaster Syria, is a stronghold of the Islamist radicals of and it is considered their de facto capital.

The activist group has documented military training of children in the city before.

Disturbing photos released in October showed boys being taught basic combat and survival skills, learning how to use assault rifles, and being given lessons in extremist ideology at a local school.

IS has been known to groom children to take part in jihad and has preyed upon the children of Raqqa, with the objective of creating an entire generation for whom Islamic extremism and acts of terrorism are normal practice.

In August, UN investigators accused IS of war crimes for using children in conflict, in a report on the war in Syria.

IBTimes' Raqqa correspondent, Zaid al-Fares, recently provided his own full and frank description of the IS child indoctrination system. You can read his account here.