The recent killing of alleged spies within the ranks of the Islamic State shows the huge risks being taken by undercover activists in Syria and Iraq who struggle to reveal to the world what it is like to be in the belly of the beast, according to a report.

Two men, identified in the brutal footage as Bashar Abdul Atheem, 20, and Faisal Hasan al-Habib, 21, donned signature orange jumpsuits and "confessed" to spying in the latest video attributed to ISIS, Fox News reported.

They were then tied to wooden posts and shot point-blank in the head.

"There are no lengthy trials," said Christoph Wilcke, Human Rights Watch's senior researcher for the Middle East and North Africa. "ISIS is quick on the trigger. The risks these people take to speak out are enormous."

It is not clear whether their admission was true or offered to protect others.

The group called Raqqa Is Being Slaughtered Silently, one of the most eminent groups that send out images and videos to the world's media agencies from inside the Syrian stronghold of ISIS, denied that it is part of the ISIS media network.

The group was formed four years ago during the public protest against Syrian dictator Bashar al-Assad. Its members were trapped in the city of Raqqa when ISIS seized control. It has digitally been sending out to the world images of executions, including that of homosexuals being thrown out of buildings and Christians being beheaded in the public.

Getting caught taking a picture in public means death, said a founding member of the group who goes by the pseudonym Abu Ibrahim Raqqawi. He himself was forced to escape to Turkey last year as the jihadists moved closer to identifying him.

"But we have some tricks to take pictures and videos to document all the crimes by ISIS," he said.

One founding member, Al Moutaz, 20, was killed in April last year after he refused to reveal the identities of those who belong in the resistance.

Another activist group called Mosul Eye secretly operates in the ISIS' stronghold in Iraq. It has been publishing photos and accounts through Facebook on teachings of the ISIS, the destruction of historical monuments, and the extremists' black market oil trade.

ISIS has started recruiting civil servants, cab drivers, salesmen and shop owners to expose and arrest these activists.

"I have learned to be secluded because not being careful with what I say and do could cause my death," said a Mosul Eye activist who goes by the name Maouris Milton.

Mosul Eye temporarily closed its Facebook page amid threats to hack it. It resumed its operations days later to reveal the "reality of what is happening in Mosul to the world," posting the names of seven people killed by ISIS.

"ISIS calls them spies, and we call them Life Makers," the Mosul Eye wrote in a post. "May your souls rest in peace, and may your souls and bodies guide and light up Mosul's way to be free of ISIL."