A report has emerged that a shadowy Sunni resistance group in Mosul, Iraq's second largest city, is hunting down Isis fighters and attacking them with sniper fire, arson and kidnapping.

A series of video clips released by the guerrilla group reveal that not everyone in Mosul has quietly accepted the dominance of the radical group, which aims to establish a Caliphate in the region, governed by Sharia law.

The footage that has been obtained exclusively by Sky News contains clips showing a resistance group member killing an Isis guard outside a building armed with an AK47. The video also has the guerrillas targeting Isis building with arson attacks.

Another part of the video reportedly shows the guerrillas in masks kidnapping an Isis senior commander. The group later claims they shot the militant leader dead after interrogation.

The secret cell, which has its operation centre based in Kurdistan, claims that it is now targeting Isis members on a "daily" basis.

"At first they were only formed into small groups but now they have been doing daily operations. They have become the ghosts which frighten Daesh (Isis) and threaten Daesh in the city," Sky News quoted a coordinator of the secret movement as saying.

The resistance group's main focus is targeting key Isis members, especially the foreign fighters. It claims that its aim is to weaken Isis from inside and it is waiting for a perfect time to launch an all-out rebellion.

The pre-dominantly Sunni city, that has a population of around two million has been under Isis control since last June. Since capture of Tikrit, the Iraqi forces have been working on a strategy to recapture Mosul from Isis.

Reports out of Mosul also have found that Isis is also preparing for a stand-off against the Iraqi forces. In the last few months, Isis has started recruiting a high number of children into its forces, as per reports.