This shadowy group is assassinating ISIS members within its borders

Iraqi Kurdish female fighters take aim against Islamic State militants in Nawaran near Mosul, Iraq, April 20, 2016.Ahmed Jadallah/Reuters

It almost seems inevitable.

With such an oppressive regime and a weakening infrastructure, the organization that touts itself as the caliphate is facing growing dissent within its civilian populace.

And it looks like this gap is widening, especially after the efforts of a secret group called the Mosul Battalions.

In Mosul, Iraq’s second largest city and one of the few remaining ISIS bastions, this secret network has been causing disarray for ISIS members by carrying out assassinations and hit-and-run strikes against ISIS targets.

In a report by CNN, online video from the Mosul Battalion has shown the capture and assassinations of ISIS members and the bombings of the militant's checkpoints.

Iraqi Kurdish female fighter Haseba Nauzad looks through a pair of binoculars during a deployment near the frontline of the fight against Islamic State

"The roadside bombs they used, they would steal from ISIS," “Abu Ali”, a Mosul Battalion intermediary told CNN. "ISIS puts bombs in certain areas and those who have previous military experience go and steal these bombs and place them to target ISIS."

After ISIS captured Mosul on June 2014, the jihadists conducted a search for weapons that were both abandoned by fleeing Iraqi soldiers as well as arms held by citizens; however, many remained hidden outside of ISIS’ grasp. It is with these rifles and pistols that the Mosul Battalion wreaks havoc for ISIS, Ali explained to CNN.

"Saddam militarized the population, all Iraqi people have weapons training,” continued Ali.

Syriac Christian female fighter Ormia pictured with her rifle

Risking torture and death, the organization claims to be so secretive that many of their members don’t know the identities of others. Contacting each other via cell phone — a crime that’s punishable by cutting the hand off the offender or even death — the rebels have developed a crude, yet effective, way of communicating.

"They work in two-person formations and a third person is at a higher level to avoid compromising the group if one is captured," he said.

Initially established by two close friends, the Mosul Battalion now claims to have between 100 and 300 fighters, many of them youth and former military members. If this figure is correct, their efforts may be invaluable in the coming months as coalition forces begin their massive campaign to liberate the city from ISIS.

The Mosul Battalion claims to have also already provided intelligence and coordinates of ISIS positions for coalition airstrikes.

Yazidi female fighter Asema Dahir, 21, holds a weapon as she rides a pick-up truck in Nawaran near Mosul, Iraq

“They wanted to work with the coalition for a couple reasons. So that the coalition is precise and doesn't hit civilian populations but also to accelerate the elimination of ISIS," said Ali to CNN.

Christian women in al-Qahtaniyah aim their weapons during training exercises

Given how past failures of the Iraqi military and US-led coalition forces led to the unintended rise of ISIS, the presence of an organic and local anti-ISIS resistance movement will be critical to the continued success of beating the militants.

Female Peshmerga fighters stand at their site near the frontline of the fight against Islamic State militants in Nawaran near Mosul, Iraq