Video released Tuesday showed captured Jordanian pilot Lt. Muath al-Kaseasbeh being burned alive by ISIS militants in Syria.
Al-Kaseasbeh, who was captured after his jet was shot down in Syria in December, is shown locked in a cage.
His orange jumpsuit appears to be doused with a liquid, possibly a flammable accelerant.
A masked militant is shown holding a flaming stick to the ground.
A trail of fire is then shown leading up to the cage.
Al-Kaseasbeh is then set on fire while locked in the cage.
The full video runs for 22 minutes and is highly produced and edited, featuring cutaways to news broadcasts detailing the pilot's capture, as well as images of bodies being pulled from the rubble of buildings.
Al-Kaseasbeh is also shown being interviewed in the first half of the video. He appears to have a bruise on his left eye.
Jordan's King Abdullah II confirmed the pilot's "martyrdom" on Twitter, announcing he was cutting short a visit to the U.S.
A spokesman for the Jordanian government said the country would deliver a "strong, earth-shaking and decisive" response to the killing.
"The revenge will be as big as the calamity that has hit Jordan," army spokesman Colonel Mamdouh al Ameri said in a televised statement, Reuters reported.
A Jordanian official told the news agency authorities would execute several militants in retaliation, including Sajida al-Rishawi, the Iraqi terrorist on death row whom the group had demanded be released.
Early Wednesday, an official confirmed that al-Rishawi's execution was scheduled for dawn, local time, the Associated Press reported.
The Jordanian pilot had been at the center of an attempted hostage swap by ISIS militants last week, and the Jordanian government repeatedly tried to gain proof from ISIS that al-Kaseasbeh was still alive.
Tweets showing images from the purported execution appear to be geotagged to Ar-Raqqah in Syria's war-torn Aleppo province.
Jordanian state television reported the pilot was killed on Jan. 3. The Jordanian general attorney has issued a gag order on publishing news of al-Kaseasbeh's death.
His family was notified by the Jordanian army on Tuesday afternoon that he had been killed.
There were also reports of protests across Jordan, particularly in the southern part of the country where al-Kaseasbeh's tribe is from. The protesters were reportedly calling for the government to avenge the pilot's death and to execute the captives ISIS wanted exchanged for his release, including al-Rishawi.
U.S. National Security spokeswoman Bernadette Meehan released the following statement to BuzzFeed News:
We are aware of the video purporting to show that Jordanian 1st Lieutenant Moaz al-Kasasbeh has been murdered by the terrorist group ISIL. The intelligence community is working to confirm its authenticity. The United States strongly condemns ISIL's actions and we call for the immediate release of all those held captive by ISIL. We stand in solidarity with the Government of Jordan and the Jordanian people.
State Department spokeswoman Jen Psaki read a version of the same statement at a press briefing.
Speaking at the White House, President Obama said that, if authenticated, the video would stand as proof the the Islamist group's "viciousness and barbarity." He added that it would serve to "redouble the vigilance and determination" of the U.S.-led coalition to destroy ISIS, which he said is "only interested in death and destruction."
The president later released the following statement:
Today, we join the people of Jordan in grieving the loss of one of their own, First Lieutenant Moaz al-Kasasbeh, cruelly and brutally killed by ISIL terrorists. On behalf of the American people, I offer my deepest condolences to Lieutenant al-Kasasbeh's family and loved ones, to the brave men and women of the Jordan Armed Forces, and to King Abdullah II and the people of Jordan.
Lieutenant al-Kasasbeh will forever personify the bravery of a true son of Jordan, one who honored his family and country by his seven years of military service. Along with his compatriots and other Arab and international members of the coalition, Lieutenant al-Kasasbeh was in the vanguard of the effort to degrade and defeat the threat posed by ISIL.
Lieutenant al-Kasasbeh's dedication, courage, and service to his country and family represent universal human values that stand in opposition to the cowardice and depravity of ISIL, which has been so broadly rejected around the globe. As we grieve together, we must stand united, respectful of his sacrifice to defeat this scourge. Today, the coalition fights for everyone who has suffered from ISIL's inhumanity. It is their memory that invests us and our coalition partners with the undeterred resolve to see ISIL and its hateful ideology banished to the recesses of history.
The video was released as Jordan's King Abdullah II was in the U.S. meeting with Secretary of State John Kerry and Vice President Joe Biden, who offered his condolences.
Earlier on Tuesday, Jordan Foreign Minister Nasser Judeh and Kerry had signed a memorandum of understanding on continued U.S. assistance to the Hashemite Kingdom. Under the terms of the agreement, the U.S. would increase its funding to Jordan from $660 million to $1 billion per year for the years 2015–2017.