The Islamic State (Isis) terrorists are facing increasing opposition inside Mosul as unidentified vigilantes are coming up with daring ways to kill Isis fighters.

Recently a man was spotted inside Mosul, who shaved his beard and stood smoking near a mosque in Mosul.

Within minutes, the Isis religious police rushed in and put him in a car, to produce him before a Sharia judge. But as the car drove away, the prisoner pulled out a gun and killed the 3 Isis fighters inside the car.

He then stepped out and drove away in another car, which was tailing all the time. The details of this Hollywood-like plot were released to the public by Mosul Eye, a former historian-turned-media activist.

According to Mosul Eye, the "secret op" was a well-planned operation carried out by anonymous Mosul-based vigilantes.

"The operation wasn't carried by a single person, it was carefully planned. There was a car escorting the [Isis prisoner] in case he might get hurt or his cover is blown," Mosul Eye revealed in a Facebook post.

The vigilantes chose the market square near Baha'uddin mosque in Alrefa'i neighbourhood as it was frequented by the Isis religious police often. The entire operation was carried out with military precision and even before other Isis members could realise what had happened, the faceless vigilantes disappeared.

Mosul Eye says this won't be the last act of the group and there will be many more such daring actions against Isis.

The Islamic State terrorists took over the second largest Iraqi city in June 2014. In the last few months, there has been increased 'vigilante' activities inside Mosul. Last month,  armed vigilantes killed five women, who were part of Isis' Al-Khansa Brigade.

The shadowy resistance group inside Mosul also carried out sniper and arson attacks on Isis. Several Isis fighters have also been kidnapped and killed by the vigilantes.

Isis also seems to be growing wary of the vigilantes. Recently, the reported that the Sunni group has banned Mosul residents from gathering in groups of more than three over fears of a 'mass uprising'.