The Islamic State group released a video on Tuesday purportedly showing a Jordanian pilot being burned alive in a cage, in the jihadists' most brutal execution yet of a foreign hostage.
The highly choreographed 22-minute video released online showed images of a man purported to be First Lieutenant Maaz al-Kassasbeh, captured in December, engulfed in flames.
King Abdullah II cut short a visit to Washington to fly home, state television said, as Amman confirmed the death of the 26-year-old fighter pilot and vowed an "earth-shattering response".
The video, whose authenticity was not immediately verified, enraged officials and the army in Jordan vowed to avenge the murder of the 26-year-old pilot.
A security official said an Iraqi would-be suicide bomber on death row, Sajida al-Rishawi, and other jihadists will be executed at dawn on Wednesday.
"The death sentence will be carried out on a group of jihadists, starting with Rishawi, as well as Iraqi al Qaeda operative Ziad Karbuli and others who attacked Jordan's interests," said the official.
State television said Kassasbeh had already been killed on January 3, before IS offered to spare his life and free a Japanese journalist in return for Rishawi's release.
United States President Barack Obama denounced the apparent killing as "just one more indication of the viciousness (and) barbarity" of IS.
The US will "redouble the vigilance and determination on the part of the global coalition to make sure" the group is "ultimately defeated", he added.
The White House said US intelligence was working to confirm the video's authenticity.
The chief of the US-led war on IS, General Lloyd Austin, condemned the pilot's murder as "savage" and vowed to "fight this barbaric enemy until it is defeated".
Activists carry posters with a portrait of the Jordanian pilot Maaz al-Kassasbeh, who was captured by Islamic State (IS) group militants on December 24 after his F-16 jet crashed while on a mission against the jihadists over northern Syria. (AFP Photo)
British Prime Minister David Cameron said the "sickening murder will only strengthen our resolve to defeat ISIL", another acronym for IS.
Kassasbeh was captured on December 24 after his F-16 jet crashed during a mission over northern Syria as part of the US-led campaign against the jihadists.
The video released Tuesday shows footage of him at a table recounting 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 video also offered rewards for the killing of other "crusader" pilots. The release of the video of Kassasbeh's purported murder came after IS beheaded two Japanese hostages within a week.
'Horrific, disgusting' footage
The Islamic State group had vowed to kill the second Japanese, Kenji Goto, and Kassasbeh by sunset on January 29 unless Amman handed over Rishawi.
Kassasbeh's plane was the first loss of an aircraft since the US-led coalition launched strikes against IS last year.
Along with Jordan, Saudi Arabia, the United Arab Emirates and Bahrain are taking part in the air strikes in Syria.
Australia, Belgium, Britain, Canada, Denmark, France and the Netherlands are participating in Iraq.
IS seized swathes of territory in Iraq and Syria last year, declaring an Islamic "caliphate" and committing a wave of atrocities.
The extremist group claimed in a video released Saturday that it had killed 47-year-old Goto, after previously murdering another Japanese hostage, Haruna Yukawa.
It 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.
Anwar Tarawneh, the wife of Jordanian pilot Maaz al-Kassasbeh, takes part in a rally in the Jordanian capital of Amman. (AFP Photo)
IS had previously beheaded two US journalists, an American aid worker and two British aid workers in similar videos.
Shiraz Maher, from the International Centre for the Study of Radicalisation at King's College London, described the footage as "simply the most horrific, disgusting thing I have seen from Islamic State in the last two years".
"They clearly want to make a real point. This is the first individual whom they have captured who has been directly involved with the Western coalition in fighting IS. It is different from the aid workers... This is an act of belligerence.
"Every time you think they cannot commit anything worse -- they open up another trapdoor."
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.
It claimed to have shot down his plane but both Jordan and the United States said it had crashed.
Kassasbeh's family had urged IS to release the recently married pilot, with his father Safi asking the jihadist group to show "mercy".