An online video has been released purportedly showing a Jordanian pilot who was captured by the Islamic State extremist group being burned to death.

The video was released on militant websites and bore the logo of the extremist group's al Furqan media service.

Jordan immediately declared it would avenge his death.

Anwar Tarawneh, the wife of Islamic State captive Jordanian pilot Muath al-Kasaesbeh, holds a picture of him.

Lt Muath al-Kaseasbeh, 26, fell into the hands of the militants in December when his Jordanian F-16 crashed near Raqqa, Syria, the de facto capital of the group's self-styled caliphate. He was the first pilot from the US-led coalition to be captured.

Following militant demands, Jordan's government had said it was willing to trade Sajida al-Rishawi, an al Qaida prisoner, for the pilot. Al-Rishawi faces death in Jordan for her role in a 2005 hotel attack that killed 60 people.

Soon after the video emerged today, Jodan said it would execute Al-Rishawi. 

"The military forces announce that the hero pilot, Muath al-Kaseasbeh, has fallen as a martyr, and ask God to accept him with the martyrs," armed forced spokesman Mamdouh al-Ameri said in a statement.

"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." 

JORDAN TO EXECUTE PRISONER

The Jordanian authorities also said they would execute "within hours" the Iraqi woman the government had sought to exchange for the pilot. 

Sajida al-Rishawi, the Iraqi woman, was sentenced to death for her role in a 2005 suicide bomb attack that killed 60 people in Amman. The authorities will also execute three men previously sentenced for militancy, the source said.

"The decision has been taken to implement the death sentence against the Iraqi convict and others," the source said, speaking on condition of anonymity.

President Barack Obama said that the video was more evidence of the group's "viciousness and barbarity".

He said it would "redouble the vigilance and determination on the part of our global coalition to make sure they are degraded and ultimately defeated."