AMMAN (AFP) - Jordan vowed to begin executing death-row Islamic extremists at dawn on Wednesday, an "earth-shattering" response to the burning alive of one of its fighter pilots by the Islamic State in Iraq and Syria (ISIS), as its King Abdullah met US President Barack Obama in Washington as the video came to light.
Mr Obama, who hosted King Abdullah in a hastily organised and brief Oval Office meeting, led widespread international condemnation of the latest graphic murder, decrying the "cowardice and depravity" of ISIS.
"The president and King Abdullah reaffirmed that the vile murder of this brave Jordanian will only serve to steel the international community's resolve to destroy ISIL," a National Security Council spokesman said after the pair met.
The Obama administration had earlier reaffirmed its intention to give Jordan US$3 billion (S$4 billion) in security aid over the next three years.
King Abdullah II recorded a televised address to his shocked and outraged nation.
The King, who was once in the military himself, described First Lieutenant Maaz al-Kassasbeh as a hero and vowed to take the battle to ISIS extremists, who have executed several captives on camera in recent months, provoking worldwide revulsion.
"Jordan's response will be earth-shattering," Information Minister Mohammed Momani said on television, while the army and government vowed to avenge the pilot's murder.
"Whoever doubted the unity of the Jordanian people, we will prove them wrong."
Hours after a harrowing video emerged online purporting to show the captive and caged 26-year-old F-16 fighter pilot engulfed in flames, a security official said executions would begin at daybreak.
Would-be Iraqi female suicide bomber Sajida al-Rishawi was named as the first slated to go to the gallows.
"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, speaking on condition of anonymity.
Lt Kassasbeh was captured in December when his jet crashed over northern Syria on a mission that was part of the US-led coalition air campaign against the militants.
Jordanian state television suggested he was killed on Jan 3, before ISIS offered to spare his life and free a Japanese journalist in return for Rishawi's release.
The White House would not speculate on whether the video was released to coincide with King Abdullah's visit to Washington.
British Prime Minister David Cameron called the murder "sickening", while UN chief Ban Ki Moon labelled it an "appalling act".
Japan's Prime Minister Shinzo Abe condemned it as "unforgivable".
The death marks a further escalation of ISIS' execution shock tactics after a series of brutal hostage beheadings.
The highly choreographed 22-minute footage shows Lt Kassasbeh at a table recounting coalition operations against ISIS, with flags from the various Western and Arab countries in the alliance projected in the background.
It then shows Lt Kassasbeh dressed in an orange jumpsuit and surrounded by armed and masked ISIS fighters in camouflage.
It cuts to him standing inside a cage and apparently soaked in petrol before a masked militant 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.
Dr 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 ISIS 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 ISIS. 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."
The release of the video came after ISIS beheaded two Japanese hostages within a week.
ISIS last year declared an Islamic "caliphate" as it rampaged across Iraq and Syria in a brutal offensive of executions and forced religious conversions.
The United States, Jordan and other nations responded with Operation Inherent Resolve, an air-led campaign to pummel the jihadist group.
Lt Kassasbeh's plane was the first loss of an aircraft since the US-led coalition launched strikes against ISIS last year.
US Central Command said that the group still had the ability "to conduct small-scale operations", despite months of air strikes.
But, it said, "their capacity to do so is degraded and their momentum is stalling".
Attacks have hit the ISIS group's "ability to command and control forces; recruit, train and retain fighters, produce revenue from oil sales, and maintain morale".