Calling for unity among extremist groups, al Qaeda leader Ayman al-Zawahri urged his followers to carry out lone wolf attacks against the United States and other Western countries in a disturbing audio recording released Sunday.
"I call on all Muslims who can harm the countries of the crusader coalition not to hesitate. We must now focus on moving the war to the heart of the homes and cities of the crusader West and specifically America," the terrorist leader said, Reuters reports.
Zawahiri, who is in hiding, encouraged Muslim youth to look to the Tsarnaev and Kouachi siblings as examples to follow when carrying out attacks against Western countries. The Tsarnaev brothers carried out the notorious Boston marathon bombings, while the Kouachi brothers are responsible for the Charlie Hebdo shootings in Paris.
"I call on all mujahedeen (Islamist fighters) in districts of Iraq and Syria to collaborate and help each other," said Zawahiri.
While it is unclear when the terrorist leader made the recording, Reuters notes that a reference to Taliban leader Mullah Mohamed Omar as still being alive dates it as at least two months old. The Afghani government announced that Omar was dead in late July.
In continuing his comments, Zawahari, a former Egyptian doctor who who replaced Osama bin Laden as the head of al Qaeda four years ago, called the Islamic State group "illegitimate."
"We have endured a lot of harm from Abu Bakr al-Baghdadi (leader of ISIS) and his brothers, and we preferred to respond with as little as possible, out of our concern to extinguish the fire of sedition," he said.
"But Abu Bakr al-Baghdadi and his brothers did not leave us a choice, for they have demanded that all the mujahideen (jihadists) reject their confirmed pledges of allegiance, and to pledge allegiance to them for what they claim of a caliphate," he added.
Despite conflict between the two groups, Zawahri issued a call for unity and emphasized that al Qaeda would join ISIS in fighting Western and secular forces in Iraq and Syria.
"If I were in Iraq or Syria I would cooperate with them in killing the crusaders and secularists and Shi'ites even though I don't recognize the legitimacy of their state, because the matter is bigger than that," he said.
Speaking to ABC News, former National Counterterrorism Center director Matthew Olsen said that Zawahri speaking out against Baghdadi "suggests that the differences are irreconcilable" between the two groups.
"It's pretty interesting," he said, "Zawahiri until now has not been willing to openly condemn Baghdadi and ISIS. It highlights how deep the division is between al Qaeda leadership and ISIS."
However, Olsen noted that had ISIS and al Qaeda realigned by joining forces, the consequences "would be terrible."
Also speaking to the news outlet, former CIA Director Michael Hayden said the U.S. could potentially use the rift between ISIS and al Qaeda to its advantage.
"It would be a good idea to do so. We always thought that the death of bin Laden could create a rift between the Egyptians and the other Arabs inside al Qaeda since Zawahiri was an Egyptian. Seems to have played out," he said.
When it comes to taking advantage of the division between two deadly extremist groups, however, Hayden cautioned, "You need to be careful."