BEIRUT: The Islamic State group released a video on Tuesday purportedly showing the burning alive of a Jordanian pilot, in the militants' most brutal execution yet of a foreign hostage.

The highly produced 22-minute video released online showed images of a man purported to be the pilot Maaz al-Kassasbeh, who was captured in December, engulfed in flames inside a metal cage.

Jordanian state television confirmed the death and said Kassasbeh had been killed on January 3, before the jihadists offered to spare his life and free a Japanese journalist in return for the release of an Iraqi would-be suicide bomber held in Jordan.

US President Barack Obama immediately denounced the purported killing.

“Should in fact this video be authentic, it's just one more indication of the viciousness (and) barbarity of this organisation,” Obama said.

He said it would “redouble the vigilance and determination on the part of the global coalition to make sure” the IS group is “ultimately defeated”.

Kassasbeh, a 26-year-old first lieutenant in the Jordanian air force, was captured on December 24 after his F-16 jet crashed while on a mission over northern Syria as part of the US-led coalition campaign against the jihadists.

The video released on Tuesday shows footage of Kassasbeh sitting at a table discussing coalition operations against IS, with flags from the various Western and Arab countries in the alliance projected in the background.

It then shows Kassasbeh dressed in an orange jumpsuit and surrounded by armed and masked IS fighters in camouflage.

It cuts to him standing inside the cage and apparently soaked in petrol before a masked jihadist uses a torch to light a trail of flame that runs to the cage and burns him alive.

The release of the video of the pilot's purported murder came days after IS beheaded a second Japanese hostage within a week.

Series of executions

IS had vowed to kill the second Japanese man, Kenji Goto, and Kassasbeh by sunset on January 29 unless Amman handed over Iraqi jihadist and would-be suicide bomber Sajida al-Rishawi, who is on death row in Jordan.

Kassasbeh's plane was the first loss of an aircraft since the coalition launched strikes against the jihadists last year.

Saudi Arabia, the United Arab Emirates, Jordan and Bahrain are taking part in the coalition air strikes in Syria.

Australia, Belgium, Britain, Canada, Denmark, France and the Netherlands are participating in Iraq.

The extremist group seized swathes of territory in Iraq and Syria last year, declaring an Islamic “caliphate” and committing a wave of atrocities.

IS claimed in a video released online Saturday that it had killed 47-year-old Goto, after previously murdering another Japanese hostage, Haruna Yukawa.

The group had initially demanded a $200 million ransom for the Japanese hostages, the same amount Tokyo had promised in non-military aid to countries affected by IS.

It had previously beheaded two US journalists, an American aid worker and two British aid workers in similar highly choreographed videos.

Jordan had vowed to do everything it could to save the pilot but had demanded proof he was still alive before handing over Rishawi.

IS had previously published what it said was an interview with the pilot in which he said his plane was hit by a heat-seeking missile.

IS claimed to have shot down his plane but both Jordan and the United States said it had crashed in an accident.

Kassasbeh's family had urged IS to release the recently married pilot, with his father Safi asking the group to show “mercy”.

After the killing of Goto, the UN Security Council on Sunday condemned the “heinous and cowardly” murder, calling for “the immediate, safe and unconditional release of all those who are kept hostage” by the group.