AMMAN, Jordan (AP) -- A video released online Tuesday purportedly showed a Jordanian pilot captured by the Islamic State extremist group in Syria being burned to death by his captors following a weeklong drama over a possible prisoner exchange.

Jordan threatened a harsh response to the killing of Lt. Muath Al-Kaseasbeh, 26, who fell into the hands of the militants in December when his F-16 crashed near Raqqa, Syria, the de facto capital of the group's self-styled caliphate. He was the only pilot from the U.S.-led coalition to have been captured to date.

King Abdullah II of Jordan, who is in Washington, spoke on Jordan TV, urging all Jordanians to unite. Confirming the pilot's death, the king said "it's the duty of all of us to stand united and show the real values of Jordanians in the face of these hardships."

However, in the pilot's home village of Ai, violent protests erupted and a local government office was set on fire. Witnesses said the situation was tense and riot police were patrolling the streets.

At a tribal meeting place where the pilot's relatives have waited for weeks for word on his fate, family members wept when receiving word of the pilot's death. Outside, hundreds of people later took to the streets, chanting: "There is no god but God and the martyr is beloved by God."

The video appeared aimed at pressuring Jordan to leave the coalition that has been battling to roll back the Islamic State group. Jordan's king, a close Western ally, has portrayed the campaign against the extremists as a battle over values, but the airstrikes against fellow Muslims are not popular in Jordan.

Jordanian government officials have said they country's continued participation in the coalition is assured, despite the hostage crisis. Officials said the killing of the pilot would only toughen Jordan's stance.

"The Jordanian response to the assassination of the hero pilot, Muath al-Kaseasbeh, will be strong, decisive and swift," government spokesman Mohammed al-Momani said in a statement carried by the official news agency Petra.

The army spokesman, Mamdouh al-Ameri, said that "our punishment and revenge will be as huge as the loss of the Jordanians."

The official Petra news agency said the king was cutting short his Washington visit and returning home.

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