The latest propaganda video released by the Islamic State (also known as ISIS or ISIL) featured the beheading of Peter Kassig, an American humanitarian aid worker who had traveled to Syria to help distressed Syrians. Kassig, who was taken hostage in October 2013 and converted to Islam while in captivity, was the third American and fifth westerner to be murdered in propaganda videos released by the Islamic State.

Kassig’s death followed that of American reporters James Foley and Steven Sotloff, as well as two British aid workers, David Haines and Alan Henning.  All of the hostages had been held in an underground prison in Raqqa, the capital city of the Islamic State’s self-proclaimed caliphate.

The Islamic State has seized at least 23 hostages from 12 different countries.  One unnamed American woman reportedly is the last remaining American hostage.

Kassig’s remains were featured in the latest sordid video.  Unlike previous videos, he did not address the camera before he was killed, perhaps because he resisted his fanatic captors.  But the aim of the propaganda exercise was the same as previous hostage videos: to incite the supporters of the Islamic State, attract more recruits and demoralize its enemies.

President Obama denounced Kassig’s beheading as “an act of pure evil.”  But his administration has been slow to take action against the Islamic State, which has metastasized and thrived in the chaos of the Syrian civil war.

The administration’s Syria policy has been a disaster that has contributed to the rapid unraveling of its Iraq policy. Even after the fall of Fallujah in January, the administration remained disengaged and paralyzed by wishful thinking.

The White House has compounded these errors by seeking Iranian cooperation in defeating the Islamic State, despite the fact that Iran poses a greater long-term threat to U.S. national security than does that fanatic movement.

Moreover, Iran’s promotion of Islamist extremism and sectarian conflict in both Iraq and Syria helped create conditions in which the Islamic State thrived and expanded. Iran’s hostile regime is an arsonist that should not be rewarded for helping to put out the fire it helped to fuel.

The Obama administration urgently needs to rethink its strategy for defeating the Islamic State.  It is still playing catch up after being caught by surprise by recent events. Peter Kassig’s death is yet another reminder that more needs to be done to destroy the Islamic State before it threatens more Americans, as well as U.S. allies in the region.