Jordan has confirmed the death of pilot Moaz al-Kasasbeh after a video published online by Islamic State (IS) claimed to show him being burned alive.
The video shows a man standing in a cage and engulfed in flames. Intelligence officials are working to confirm it is genuine.
Jordan vowed “punishment and revenge”.
Lt Kasasbeh was captured when his plane came down near Raqqa, Syria, in December on a mission to support the US-led military coalition against IS.
The video posted online on Tuesday was distributed via a Twitter account known as a source for IS propaganda.
The highly produced 22-minute film includes a sequence showing the Jordanian pilot walking at gunpoint amongst rubble apparently caused by coalition air strikes that targeted jihadists.
The BBC’s security correspondent Frank Gardner says the new and horrific video is aimed at a world already shocked by the calculated cruelty of Islamic State’s actions,
Jordanian state TV reports that Lt Kasasbeh, 26, was killed a month ago – since when Jordan has continued attempts to secure his release.
Jordan had been attempting to secure Lt Kasasbeh’s release as part of a prisoner swap, offering to free Iraqi militant Sajida al-Rishawi in exchange.
She is a failed suicide bomber now on death row in Jordan for her role in attacks in the capital, Amman, that killed 60 people in 2005.
‘Not in vain’
IS had sought Rishawi’s release in exchange for that of captive Japanese journalist Kenji Goto. A video that appeared to show Goto’s dead body appeared three days ago.
A spokesman for the Jordanian armed forces, Mamdouh al-Ameri, said Lt Kasasbeh had “fallen as a martyr”.
“While the military forces mourn the martyr, they emphasise his blood will not be shed in vain. Our punishment and revenge will be as huge as the loss of the Jordanians.”
Kevin Connolly, BBC Middle East Correspondent
The male members of the al-Kasasbeh family had been gathering every day at a community centre not far from the royal palace in Amman. Cousins, brothers and uncles maintained a vigil of support for Moaz’s father, who sat anxious but dignified in a red chequered headdress and long flowing black robe.
After the murder of Japanese journalist Kenji Goto the mood darkened, and one of the pilot’s uncles, retired police general Fahd al-Kasasbeh, was close to tears as he asked the BBC to help relay a direct appeal to the hostage-takers.
There were family members who hoped Lt Kasasbeh would be treated with lenience because he was a Muslim, while others feared he would be harshly dealt with as an enemy pilot. And all along on both sides of the argument was the nagging fear that no proof of life was received, no photographs and no video.
The family’s reaction, of course, will be one of deep grief and distress. But in wider Jordanian society, there will be pressure for the government to hit back. An implicit threat to speed up the execution of IS prisoners in Jordanian jails, where some are already on death row, may now be carried out.
Jordan’s King Abdullah cut short a visit to the US after news of Lt Kasasbeh’s death.
US President Barack Obama said in a statement that if the video was real, it would be “one more indication of the viciousness and barbarity” of IS.
“I think it will redouble the vigilance and determination on the part of the global coalition to make sure they are degraded and ultimately defeated,” he added.
Gen Ali Shukri, a former Jordanian army officer, told the BBC the news would cause “total dismay” in Jordan.
“This is something that hasn’t been seen before,” he said.
“It’s an absolute terror. Now the very old saying of an eye for an eye and a tooth for a tooth is going to be brought back, and I think days ahead of us will show that to [IS] and whoever is supporting them.”
Timeline: Jordanian pilot held hostage
24 December 2014: Jordanian Lt Moaz Youssef al-Kasasbeh captured by IS after his plane crashes
25 December 2014: Pilot’s father urges IS to show mercy
20 January 2015: IS threatens to kill two Japanese hostages unless Japan pays $200m ransom within 72 hours
24 January: IS releases video of Japanese hostage Kenji Goto holding a picture Haruna Yukawa’s decapitated body
24 January: IS calls for release of Sajida al-Rishawi, an Iraqi militant sentenced to death in Jordan
28 January: Jordan offers to release Rishawi in exchange for Lt Kasasbeh
29 January: Deadline to kill Lt Kasasbeh and Mr Goto expires
31 January: Video released appearing to show Kenji Goto’s body
3 February: Video released appearing to show Lt Kasasbeh burnt alive