ISIS jihadists were paid well for their service, documents belonging to the terrorist group, and obtained by RT in Iraq, reveal. Use of chemical agents was paid-for in silver, while taking down a chopper was rewarded with gold.

Despite the common belief that Islamic State (IS, formerly ISIS/ISIL) fighters were often forced to join the terrorist group or were recruited based on the conviction of their faith to carry out jihad, documents from the Iraqi city of Mosul and seen by RT show that fighting for the self-proclaimed caliphate also had its financial incentives.

Joining the ranks of the well-organized terror network, which once proclaimed a self-styled caliphate on the territory of Syria and Iraq, was only possible through a letter of recommendation, where the new recruit was carefully evaluated based on his military and sharia training.

Once in, the recruits remained under the meticulous watch of IS commanders, who kept tabs on their deployments, munition, supplies and eventual death. Those who served in the army of terror loyally and faithfully were rewarded – or were at least promised a reward. For instance, those who managed to take down an aircraft were promised a car. To destroy an enemy helicopter or drone earned at least seven gold dinars, according to the accounting records seen by RT Arabic.

Using chemical weapons had way less merit for IS, which paid only 10 silver dinars to its fighters to fire a projectile filled with a chemical warfare agent. Mustard gas and other toxic substances were used by IS in the vicinity of the Kirkuk, Fallujah, and Tikrit areas, an Iraqi investigation into the use of chemical weapons reports, RT has discovered.

READ MORE: ISIS offering potential recruits protection, payments & free passage to Europe – think tank

Thousands of fighters, along with their families, joined IS at the height of the group’s activity in Iraq and Syria. Most of them came from within Iraq, while others came from across the region, the IS documents kept by Iraq's army intelligence showed. “A huge number of militants arrived in Iraq from other countries. You can talk about hundreds of thousands of people, including the families of terrorists – wives and children who were smuggled illegally into Iraqi territory,” Lieutenant Colonel Jaber Assad told RT Arabic.

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