By Catherine Philp and Sara Elizabeth Williams

King Abdullah vowed “relentless war” against Islamic State yesterday, promising to ramp up his country’s role in the American-led military coalition amid outrage over the videotaped immolation of a young Jordanian pilot.

He spoke hours after Jordan executed two jihadist prisoners in ­retaliation for the grisly killing of Flight Lieutenant Muath al-Kasaesbeh, who was burnt alive in a cage. “We are waging this war to protect our faith, our values and human principles, and our war for their sake will be relentless and will hit them in their own ground,” state television quoted him as saying to cheering crowds after landing in Amman, having cut short a trip to Washington.

He went straight from the airport to a meeting of military officials to discuss Jordan’s response. A government spokesman said officials had agreed that Jordan should intensify its participation in the coalition as part of a “collaborative effort” to defeat Isis. “Jordan’s response will be heard by the world at large,” the spokesman said.

Duncan Hunter, a Republican congressman who met the king in Washington after the video emerged, described him as “visibly enraged” and determined to up the ante militarily against Isis. “He said there is going to be retribution like Isis hasn’t seen,” Mr Hunter told the Washington Examiner. “The only problem we’re going to have is running out of fuel and bullets,” he quoted King Abdullah as saying.

Jordan’s first act of vengeance came swiftly, before dawn yesterday, with the executions of Sajida al-Rishawi and Ziad Karbouli at a prison south of Amman. Rishawi was a failed female suicide bomber for Isis’s forerunner, al-Qaeda in Iraq, whose brother was the right-hand man of its founder, Abu Musab al-Zarqawi.

Karbouli was also a close aide of Zarqawi and had been sentenced to death for a terrorist plot to kill Jordanians in Iraq. Both had been possible candidates for a prisoner swap with Isis.

Ziad Alzoubi, a spokesman for ­Jordan’s interior ministry, said the ­executions were meant to send a message about terrorism and were not just an act of revenge. They were also widely seen as a means to calm public anger over the pilot’s brutal killing. Crowds spilled into the streets in the hours after the video emerged, with calls for vengeance against both Isis and the al-Qaeda prisoners — but with many others ­casting blame on Jordan’s king.

World leaders, including many from the Arab world, were quick to denounce the manner of the pilot’s death. Many prominent Muslim clerics condemned it as being against Koranic teaching, which prohibits the burning of humans alive or dead, including cremation.

Mr Alzoubi said that the bodies of the two executed prisoners would be given full Muslim burials. “The bodies will be buried and will not be maimed nor burnt, because this is the kind of morals Jordan has,” he said.

In Raqqa, Syria, the capital of the Isis “caliphate”, giant screens were erected in public squares to show the gruesome video of Flight Lieutenant Kasaesbeh’s killing to cheering crowds. In another video released by Isis, residents voiced their approval of the killing.

A young boy, calling himself Abou al-Laith, said: “I’m so happy because they burnt him — I would have burned him myself. I wish other pilots come so we can catch them and burn them too.”

Anti-Isis activists in Raqqa identified the location where Flight Lieutenant Kasaesbeh was killed as the site of a coalition air strike in which many women had burnt to death.

Beneath a sprawling tent in Karak, the pilot’s home region, his extended family received condolences yesterday from a long line of friends, tribesmen and dignitaries. Scores of uniformed military men arrived and left en masse, including Flight Lieutenant Kasaesbeh’s air force colleagues.

Members of the Kasaesbeh tribe make up a significant proportion of ­Jordan’s military and police forces. Ali, 17, said that Flight Lieutenant Kasaesbeh’s death had stoked his desire to join Jordan’s armed forces.
“The word ‘animals’ is too small for [Isis],” he said. “Inshallah I will join the army and avenge his death. Most boys here want that.”

Most of the boys gathered round Ali agreed. Only one, Ahmad, 14, admitted that he would rather be a police officer, so he wouldn’t have to leave Jordan and fight abroad. “I’m scared to join the army,” he said in a soft voice. “I’m scared because of what happened to Muath.”

The murder of the pilot has raised new fears for the lives of Isis’s remaining foreign hostages.

A British journalist, John Cantlie, and a 26-year-old American woman aid worker are thought to be among half a dozen hostages still being held.