ISIS beheading Libya
Isis beheaded 21 Egyptian Coptic Christians in Libya earlier this monthReuters

An Egyptian hacker who claimed to have gained access to the computers of Islamic State (Isis) radicals said only a fraction of the extremist organisation's execution videos has been released.

Egyptian software engineer Ahmad Samara said stored in the databases of the jihadist group were numerous out-takes, and evidence of the involvement of English-speaking producers in creating the propaganda videos, in which prisoners, Western hostages and members of minority groups have been subjected to brutal executions.

"I entered all the Isis files and I found where they store their beheading, burning and killing videos," Samara told the Arabic language service of Al-Arabiya, in an interview quoted by Rudaw. "I was appalled by what I saw."

Tracking the group's server through the websites it posts its execution videos on, Samara said he was last able to hack IS on 3 February.

He said among the material IS had on the server were unreleased executions videos and out-takes from its horrific film of Jordanian pilot Moaz al-Kasasbeh being burned alive in a cage earlier in February, in which an American-accented producer shouts at the militants in the film in order to get the right angle for a shot.

"Filming the burning of Moaz had taken a long time and the producer is seen shouting at them to take more takes for a better angle. I saw foreign producers who spoke fluent English and from his accent I could tell that one of them was American," Samara told Al-Arabiya.net.

Samara said that among the videos was that showing the execution of 21 Egyptian Coptic Christians and he did not know who the victims were at the time because the kidnapping of the Christians had not been reported.

He said the video had been carefully edited, with sound effects added, and five cameras used to record the killings. "I saw in the video the martyrs screaming as they are beheaded," he said.

Videos of executions and burnings of other foreign nationals have not yet been released, Samara pointed out.

He said that after hacking the website, he left a picture of al-Kasasbeh standing before the miltiants, with the caption "stand tall – you are a lion among dogs".