An image from a video released in 2012 by al-Qaeda’s media arm, courtesy of the Site Intelligence Group, shows al-Qaeda leader Ayman al-Zawahiri. In his most recent audio message, he condemned the Islamic State for causing splits among jihadists. (AFP/Getty Images)

In a newly publicized audio message, al-Qaeda leader Ayman al-Zawahiri has condemned the Islamic State for attempting to pull jihadists away from other militant organizations to join its self-proclaimed caliphate.

Zawahiri, the Egyptian doctor who assumed the leadership of al-Qaeda after the killing of Osama bin Laden in 2011, has previously chastised leaders of the rival Islamist group, whose domain now stretches across much of Iraq and Syria. But his new comments may reflect the growing vulnerability of al-Qaeda, which after years of rallying militants across the world has been overshadowed by the Islamic State.

The message, produced by al-Qaeda’s as-Sahab media foundation, was recorded this spring and posted on jihadist Web forums Wednesday, according to SITE Intelligence Group.

“We have endured a lot of harm from Abu Bakr al-Baghdadi and his brothers, and we preferred to respond with as little as possible, out of our concern to extinguish the fire of sedition,” Zawahiri said, according to a translation provided by SITE. Baghdadi, a veteran Iraqi militant, has declared himself caliph of a group which now boasts several franchises.

“But Abu Bakr al-Baghdadi and his brothers did not leave us a choice, for they have demanded that all the mujahideen reject their confirmed pledges of allegiance, and to pledge allegiance to them for what they claim of a caliphate,” he said.

Even as Islamic State operations crop up in places such as Libya and Yemen, sporadic battles continue in Syria and elsewhere between militants linked to al-Qaeda and those from the Islamic State.

But Zawahiri also appeared to leave open the possibility of collaboration with Islamic State fighters, whose battlefield success has prompted a growing U.S.-led military campaign over Iraq and Syria.

“Despite the big mistakes (of the Islamic State), if I were in Iraq or Syria I would cooperate with them in killing the crusaders and secularists and Shiites even though I don’t recognize the legitimacy of their state, because the matter is bigger than that,” he said, according to a report from Reuters.

Both al-Qaeda and the Islamic State are Sunni Muslim groups that regard Shiites as infidels.