Beirut (AFP) - By burning a Jordanian pilot alive in its most savage execution video yet, the Islamic State (IS) group aims to terrify its Arab and Western opponents into ending their anti-jihadist war.

Already infamous for beheading and stoning to death its victims, IS is trying to "up the ante" with the latest execution, experts said.

With the murder of an airman participating in the US-led coalition fighting IS, the jihadists hope to sow division and fear among their opponents.

"It is a message for the coalition... your men will end up in videos that are even more horrific and will do lasting damage to public opinion in your countries," said Romain Caillet, an expert on jihadist movements.

No "head of state wants to see a young soldier end up in one of these videos," he said.

Jordanian pilot Maaz al-Kassasbeh was captured by IS in December when his fighter plane crashed in Syria as he participated in the US-led campaign against the group.

Amman said publicly that it was willing to free an Iraqi female jihadist on death row in exchange for Kassasbeh and a Japanese journalist being held by IS.

But Jordanian state media said Tuesday that Kassasbeh appeared to have been killed on January 3, suggesting the group never planned to exchange the pilot.

It preferred instead the shock and propaganda value of killing him, said Hassan Hassan, an expert at the Delma Institute, a research centre based in Abu Dhabi.

- 'Maximum pain' for coalition -

"It was a huge opportunity for IS to inflict maximum pain on the international coalition, especially to Muslim countries that took part in it," he said.

"The main purpose of this video is to send a message that retribution against fellow Muslims who assist the United States in its fight against the group will be unimaginable."

Iraq-based security expert Hisham Alhashimi agreed, saying the gruesome execution method was intended to evoke the maxim "an eye for an eye".

"IS wants to terrorise the Jordanian air force and say that any pilot who falls into their hands will meet the same fate," he said.

Story continues

"As the pilot brought down fire on the jihadists (with air strikes), so they burned him according to the law of an eye for eye," Alhashimi said.

Even for a group infamous for its brutality, the execution of Kassabeh marked a significant escalation.

Thomas Pierret, a Syria specialist at the University of Edinburgh, said the group was being forced to "innovate" to gain maximum effect.

"They are operating within the logic of the news cycle, where the public becomes used to everything and they have to 'innovate' to get attention," he said.

"IS has used beheadings so often that they have become almost banal. Burning a prisoner alive is a way to get maximum 'buzz', as it were."

The video, more than 22 minutes long, seeks to justify burning Kassasbeh alive by showing footage of the air strikes launched by the US-led coalition in Syria since September.

"Burning alive is a sort of response to the 'fire from the sky' that F-16 jets represent," Pierret said.

- Muslim backlash against killing -

The video also includes quotes from the radical 13th century scholar Ibn Tamiyya, a favoured theologian of Islamic fundamentalists and extremists, intended to justify the mode of execution.

"If a horrible death... enables you to repel aggression... it is a legitimate jihad," the quote superimposed on Kassasbeh's burning body reads.

And online, jihadist sympathisers shared documents in Arabic and other languages with "proofs" that burning Kassasbeh alive was religiously justified.

But Islamic scholars accused the group of violating religious law and cherry-picking from religious verses to justify their brutality.

They pointed to jihadist references to a Koranic verse stating: "If you punish (an enemy), punish them with the equivalent of that with which you are harmed."

The rest of the verse, which the jihadists ignore, continues: "But if you are patient, it is better".

Others pointed to sayings of the Prophet Mohamed that prohibit torture and death by burning.

Hassan said the video could end up backfiring, turning even ambivalent Muslims against IS.

In Jordan, he said, even fundamental Muslims "who showed no qualms about the fate of the pilot, objected to the manner in which he was killed and presented."