Beirut (AFP) - Brutal beheadings recorded on video by the jihadist Islamic State are intended to terrorise the group's enemies, but are also angering and alienating the Muslims the group claims to represent.
On Tuesday, the jihadist group released a new video purporting to show the beheading of Steven Sotloff, the second US journalist to be decapitated by its fighters in a fortnight.
The video was described as "sickening" by the United States and provoked widespread anger as well as fear -- which experts say is precisely the group's intention.
For Rita Katz, director of extremist monitoring group SITE, releasing videos of the beheadings of Sotloff and journalist James Foley before him "has a straight-forward purpose from an analytical standpoint: intimidation".
"The brutality demonstrated in the video says, 'Don't mess with us.'"
The Islamic State claim "to be the only 'true Muslims' and resort to murder and mayhem as a psychological tactic to terrorise other people," said Asma Afsaruddin, a professor at Indiana University's religious studies department.
Beheading has become almost a calling card for IS, which has used the method on opponents ranging from Syrian and Iraqi government troops to activists who have opposed its abuses.
As well as the two US journalists, in the last two weeks IS has also released videos of a Lebanese soldier and a Kurdish fighter being beheaded.
The method has clearly been effective in spreading fear: when the group advanced in Iraq this year, hundreds of thousands fled in terror.
- Re-emerging tactic -
As a tactic, decapitation by jihadists is not new -- extremists beheaded US journalist Daniel Pearl in Pakistan in 2002.
It also became a favoured method of Al-Qaeda's Iraqi affiliate, a precursor of today's Islamic State, under the leadership of militant Abu Musab al-Zarqawi.
With Zarqawi's death in a US raid in Iraq in 2006 and the weakening of his group, its use declined.
But with the emergence of the Islamic State, which has broken with Al-Qaeda and declared its own Islamic "caliphate" in Syrian and Iraqi territory, decapitation has once again become a potent tool.
Katz said videos of the brutal tactic also served the "alarming" purpose of "recruitment to jihad," by attracting a small minority of radicalised Muslims impressed by such violent excesses.
"A dangerous community with a dark view of the world has interpreted the video in a celebratory and empowering vein," Katz wrote in an analysis for the group.
But for most in the Muslim world and elsewhere, the Islamic State's tactics produce revulsion and anger.
"The acts and practices of IS in terms of beheadings and insulting minorities are at complete odds with the message of Islam and Muslim belief," said Sheikh Khaldun Araymit, secretary-general of Lebanon's Supreme Islamic Council.
"Islam is mercy and love and communication with the other," he told AFP.
"The heinous acts carried out by IS not only contradict Islam but are offensive to it."
- 'No basis' in Islamic law -
Muslims express similar feelings online, taking to Facebook and Twitter after each new IS outrage, whether the crucifixion of Syrians or the reported trafficking of Yazidi women kidnapped in Iraq.
Scholars of Islam say there is no crime for which beheading is religiously prescribed, though the tactic was used in war by Muslims and non-Muslims alike at the time of Prophet Mohammed and after.
"Beheading certainly was the common way to carry out criminal prosecutions throughout Islamic history, and it therefore was the default," said Haider Ala Hamoudi, an Islamic law expert and professor at Pittsburgh University law school.
"The custom developed among peoples who were aware that it was on balance much less painful than other available means of execution."
Beheading remains in use in Saudi Arabia, but Araymit noted that there it is used only "after a trial in the presence of a judge and where a pardon is not given."
Rights groups have criticised its continued use there however, and accused the Saudi judicial system of serious flaws.
Officials at Egypt's prestigious Al-Azhar religious authority have rejected the Islamic State and its practices as un-Islamic.
"These criminal acts have nothing to do with Islam" Azhar official Abbas Shoman told AFP. "There is no basis for them in Islamic law."
"These people do not represent Islam," he added.
Online and on television, Muslims have been increasingly responding to IS atrocities.
Twitter user @LibyaLiberty, writing after Foley's killing, said: "If you think Muslims aren't condemning ISIS.. you're not listening to Muslims."
"Feel free to quote: 'I, a Muslim, do hereby condemn ISIS for cutting off the heads of people, including mine, if they could'," she said, using another name for the extremist group.