New ISIS Spokesman Is a Little-Known and Dangerous Mouthpiece

On September 12, the Pentagon confirmed what it had achieved in a Syria airstrike two weeks earlier: the killing of the Islamic State (ISIS) militant group's chief propagandist and strategist, Abu Mohammad al-Adnani.

More than three months passed since his death before the radical Islamist group named a successor. That announcement came in a 24-minute audio recording posted online on Monday, in which the ISIS-linked Furqan media branch named Adnani's successor as Abu Hassan al-Muhajir, whose appearance and location remain unknown.

Adnani, a 39-year-old Syrian, spearheaded ISIS's propaganda output of gruesome beheading videos and massacres that meant it overtook Al-Qaeda as the world's best known jihadi group. He also presided over the group's external operations arm, a secretive branch known as the Emni, which plotted attacks around the world. ISIS did not publicly reveal this role, but authorities discovered it through detained ISIS fighters. It made Adnani one of ISIS's most notorious militants, one worth a $5 million U.S. bounty.

His most notorious act was his call in September 2014 for the group's Muslim supporters around the world to attack Western kuffar , or disbelievers, wherever they could, and with whatever weapon they could muster. "Smash his head with a rock, or slaughter him with a knife, or run him over with your car," he said in an audio message.

This is the message that security services in the West believe went on to inspire individual attacks in San Bernardino, Orlando, Nice and Copenhagen. Adnani reiterated this call for local attacks in a similar address before Ramadan in June.

While little is known about Adnani's successor, al-Muhajir has immediately done the same, issuing an almost identikit call for attacks on the soil of Western nations. In the audio message, he called on sympathizers to "redouble your efforts and step up your operations" in countries outside the group's control.

"He is focused on amplifying a set of key narratives that have manifested in extraordinary security problems for the West: All Muslims must pledge allegiance to the group's 'caliph,' al-Baghdadi, and allegiance is affirmed through action—waging jihad against the group's enemies 'wherever you find them,'" says Michael S. Smith II, co-founder of U.S.-based Kronos Advisory.

"Attack them inside their houses, markets, roads, and clubs and burn the land under their feet," Muhajir continued in his call, following Adnani's instruction for random attacks on soft targets, as opposed to traditional military or diplomatic targets.

Some commentators, such as Rita Katz of monitoring service SITE Intelligence, have suggested that Muhajir may not be the real identity of the spokesperson, in order to protect his safety. Experts suggest that the use of a new spokesman takes some of the pressure off of leader Abu Bakr al-Baghdadi to rouse support abroad, and minimizes the chances of him being located by the U.S.-led coalition.

"The continued use of a spokesperson—a proxy of the 'caliph'—reflects the group's efforts to engineer the perceptibility of a legitimate governing enterprise, or 'caliphate.' This is all about looking official," Smith says. "The use of a spokesman reduces the need for Baghdadi to be more involved with a key aspect of the group's activities: demanding support while commanding violence against the group's enemies the world over."

Promoting a message of defiance, Muhajir said that a myriad of international forces had failed to defeat the group in its self-declared caliphate in Iraq and Syria, despite that very entity appears close to falling with the Iraqi-U.S. offensive on its northern Iraqi city of Mosul. He ordered ISIS supporters to target Turkey in apparent revenge for Ankara's operation against the group in Syria.

"[Attack] the secular, apostate Turkish government in every security, military, economic and media establishment, including every embassy and consulate, that represents it in all countries of world," he said. The call to target Turkey is a similar call to arms that Baghdadi issued previously.

"Destroy their vehicles, raid them…in their shelters so they can taste some of your misery and do not talk yourselves into fleeing," Muhajir said.

Related: Who was the ISIS propaganda chief killed by a U.S. airstrike?

It remains unclear whether Muhajir will take the reins of ISIS's external operations arm, or has the capacity to plot and direct attacks abroad. It is possible that he has previous experience in ISIS's communication operations in Iraq or Syria, potentially working under Adnani. ISIS has developed an extensive propaganda system in which its Amaq news agency pumps out material likely sourced from operatives around the caliphate, according to experts, as well as propaganda videos and recordings created within ISIS-held territory.

European security services were already concerned and preparing for further individual attacks after Adnani's death as his deadly message lives on among a supporter base on the continent that could now include hundreds of returning foreign fighters from Iraq and Syria as the group continues to suffer defeats on the battlefield. With the introduction of Muhajir, the sheen of an official jihadi group and its brutal message has been reinforced, potentially with deadly consequences.