"The laxity of the international community in dealing with a president who kills his people … is what created these extremist groups and provided them with a fertile environment," he said, alluding to Syria’s President Bashar Assad.
Hussein Bin Mahmoud, an Islamic State-linked theologian, claimed on one of the group’s social media forums that two of the Prophet Muhammad’s revered successors ordered punishment by fire for Arab renegades in the seventh century. Al-Azhar says the claim is unsubstantiated.
Bin Mahmoud also cited a Quranic verse that requires Muslims to punish their enemies in kind. Since U.S.-led airstrikes "burn" Muslims, he argued, the IS group must burn those behind the raids.
But that’s a view that has only been embraced by a radical fringe, with mainstream Muslims united in condemnation. Iyad Madani, the leader of the 57-nation, Saudi-based Organization of Islamic Cooperation — the world’s largest bloc of Muslim countries — condemned the killing.
It "utterly disregards the rights of prisoners Islam has decreed, as well as the human moral standards for war and treatment of prisoners," a statement from Madani said. It is sad to see "the depth of malaise" in parts of the Middle East, along with the "intellectual decay, the political fragmentation and the abuse of Islam, the great religion of mercy."
U.S.-allied Gulf Arab nations issued similar condemnations.
The foreign minister of the United Arab Emirates, Sheikh Abdullah bin Zayed Al Nahyan, condemned the killing and reaffirmed his nation’s commitment to fighting terrorism and extremism. "This heinous and obscene act represents a brutal escalation by the terrorist group, whose evil objectives have become apparent," he said.
The UAE is one of the most visible Arab members in the U.S.-led coalition battling the Islamic State group, which also includes Jordan. Bahrain, a Gulf state that is home to the U.S. 5th Fleet, denounced the killing as "despicable," and Kuwait’s emir, Sheikh Sabah Al Ahmad Al Sabah, blasted the killing as "criminal" and "vicious."
Qatar’s Foreign Ministry also condemned the "criminal act." The tiny but very rich Gulf nation hosts the regional command center coordinating coalition airstrikes.
In predominantly Muslim Turkey, President Recep Tayyip Erdogan called the killing an act of "savagery."
"There is no such thing in our religion … and they have nothing to do with Islam," he said.
Iran, which has aided both Iraq and Syria against the IS group, said the killing of the pilot was an "inhuman" act that violated the codes of Islam, according to a statement by Foreign Ministry spokeswoman Marziyeh Afkham.
Religious and political leaders across the Muslim world have condemned past atrocities committed by the Islamic State group, including the beheading of foreign journalists and aid workers, and the mass killing of captured Iraqi and Syrian soldiers.
But the killing of al-Kaseasbeh, who had been the subject of intense negotiations over a possible swap with an al-Qaida prisoner on death row in Jordan, seems to have hit much closer to home. The prisoner, an Iraqi woman convicted of involvement in a triple hotel bombing in Amman in 2005, was executed along with another al-Qaida prisoner at dawn on Wednesday.
The pan-Arab al-Hayat newspaper led its coverage of the pilot’s killing with a one-word front-page banner: "Barbarity."
"How many … are there, whose names we are ignorant of, slaughtered by the Islamic State and their brothers?" asked an article in the left-leaning Lebanese daily Assafir. "How many Syrian al-Kaseasbehs have fallen in the past four years … without news headlines on the television channels?"
Jordanian politician Mohammed al-Rousan wept on television as he described watching al-Kaseasbeh’s death, saying even people attuned to violence could not bear to see a man burned alive.
But in an instant his grief turned to rage.
"Let’s use the same methods as them!" he shouted during the interview with Lebanon’s al-Mayadeen TV. "Let’s kill their children! Let’s kill their women!"
The Associated Press contributed to this report.