New York, Dec 18 (IANS): The Islamic State (IS) Sunni terror group uses unparalleled violence and brutality in its quest to achieve primacy over rival Shia Muslims and facilitate restoration of an Islamic Caliphate, says a study, co-authored by two retired FBI agents.

The group uses extreme violence and brutality against anyone it perceives as a threat to its goal, said the authors, noting that gratuitous violence has become the organisation's "brand".

The most defining characteristic of IS "is its proclivity to use extreme violence against anyone whom it perceives to be a threat to its continued expansion. It makes little distinction between combatants or civilians, men or women," co-authors Thomas Neer and Mary Ellen O'Toole noted.

The most spectacular example of IS's murderous behaviour are beheadings, which it has recorded live and later uploaded on internet.

On a practical level, the group believes that murders committed in this manner will facilitate its demands for ransom, discredit transitional states, discourage foreign investments, and help attract new recruits, the authors explained.

From a psychological perspective, these gruesome and ritualistic murders inspire intense, long-lasting psychological effects, bestowing IS with enormous attention and publicity, they added.

"IS is a global concern on many levels, and its grandiose display of extreme and ruthless violence is stunning," O'Toole pointed out.

"In this article, my colleague and I provide a behavioural assessment of this dangerous and evolving group comprised largely of young men in a vulnerable age group - late teens and twenties," O'Toole added.

The review appeared in the journal Violence and Gender.